diff --git a/lang/llvm-17/Portfile b/lang/llvm-17/Portfile
index d567453e31e4b..c88c52f80360b 100644
--- a/lang/llvm-17/Portfile
+++ b/lang/llvm-17/Portfile
@@ -29,7 +29,7 @@ version                 ${llvm_version}.0.6
 name                    llvm-${llvm_version}
 revision                1
 subport                 mlir-${llvm_version}  { revision [ expr ${revision} + 0 ] }
-subport                 clang-${llvm_version} { revision [ expr ${revision} + 2 ] }
+subport                 clang-${llvm_version} { revision [ expr ${revision} + 3 ] }
 subport                 lldb-${llvm_version}  { revision [ expr ${revision} + 1 ] }
 subport                 flang-${llvm_version} { revision [ expr ${revision} + 1 ] }
 
@@ -224,6 +224,16 @@ if {${os.platform} eq "darwin" && ${os.major} <= 16} {
     patchfiles-append 0042-mbstate_t-not-defined.patch
 }
 
+if {${os.platform} eq "darwin" && ${os.major} < 19} {
+    # https://trac.macports.org/ticket/68522
+    # Undefined symbols for architecture x86_64:
+    #   "__availability_version_check", referenced from:
+    #       ___isPlatformVersionAtLeast in libclang_rt.osx.a(os_version_check.c.o)
+    #       __initializeAvailabilityCheck in libclang_rt.osx.a(os_version_check.c.o)
+    # Upstream discussion at https://reviews.llvm.org/D150397
+    patchfiles-append 0130-10.14-and-less-availability.patch
+}
+
 post-patch {
     reinplace "s|@@PREFIX@@|${prefix}|" \
         ${patch.dir}/clang/lib/Driver/ToolChains/Clang.cpp \
diff --git a/lang/llvm-17/files/0130-10.14-and-less-availability.patch b/lang/llvm-17/files/0130-10.14-and-less-availability.patch
new file mode 100644
index 0000000000000..eebb85b11ff42
--- /dev/null
+++ b/lang/llvm-17/files/0130-10.14-and-less-availability.patch
@@ -0,0 +1,32 @@
+This is a conditional revert of https://github.com/llvm/llvm-project/commit/b653a2823fe4b4c9c6d85cfe119f31d8e70c2fa0.
+__attribute__((weak_import)) does not prevent Undefined symbol error.
+
+--- a/compiler-rt/lib/builtins/os_version_check.c.orig	2023-11-28 09:52:28.000000000 +0100
++++ b/compiler-rt/lib/builtins/os_version_check.c	2024-08-28 18:19:16.000000000 +0200
+@@ -86,9 +86,11 @@
+                                             CFStringEncoding);
+ typedef void (*CFReleaseFuncTy)(CFTypeRef);
+ 
++#if MAC_OS_X_VERSION_MIN_REQUIRED >= 101500
+ extern __attribute__((weak_import))
+ bool _availability_version_check(uint32_t count,
+                                  dyld_build_version_t versions[]);
++#endif
+ 
+ static void _initializeAvailabilityCheck(bool LoadPlist) {
+   if (AvailabilityVersionCheck && !LoadPlist) {
+@@ -98,8 +100,14 @@
+   }
+ 
+   // Use the new API if it's is available.
++#if MAC_OS_X_VERSION_MIN_REQUIRED >= 101500
+   if (_availability_version_check)
+     AvailabilityVersionCheck = &_availability_version_check;
++#else
++  // __attribute__((weak_import)) does not prevent Undefined symbol error on 10.14
++  AvailabilityVersionCheck = (AvailabilityVersionCheckFuncTy)dlsym(
++      RTLD_DEFAULT, "_availability_version_check");
++#endif
+ 
+   if (AvailabilityVersionCheck && !LoadPlist) {
+     // New API is supported and we're not being asked to load the plist,
diff --git a/lang/llvm-18/Portfile b/lang/llvm-18/Portfile
index 78883b9040828..2ad5001c3e98e 100644
--- a/lang/llvm-18/Portfile
+++ b/lang/llvm-18/Portfile
@@ -29,7 +29,7 @@ version                 ${llvm_version}.1.8
 name                    llvm-${llvm_version}
 revision                0
 subport                 mlir-${llvm_version}  { revision [ expr ${revision} + 0 ] }
-subport                 clang-${llvm_version} { revision [ expr ${revision} + 3 ] }
+subport                 clang-${llvm_version} { revision [ expr ${revision} + 4 ] }
 subport                 lldb-${llvm_version}  { revision [ expr ${revision} + 1 ] }
 subport                 flang-${llvm_version} { revision [ expr ${revision} + 1 ] }
 
@@ -181,6 +181,16 @@ if {${os.platform} eq "darwin" && ${os.major} <= 16} {
     patchfiles-append 0041-no-Werror-unguarded-availability-new.patch
 }
 
+if {${os.platform} eq "darwin" && ${os.major} < 19} {
+    # https://trac.macports.org/ticket/68522
+    # Undefined symbols for architecture x86_64:
+    #   "__availability_version_check", referenced from:
+    #       ___isPlatformVersionAtLeast in libclang_rt.osx.a(os_version_check.c.o)
+    #       __initializeAvailabilityCheck in libclang_rt.osx.a(os_version_check.c.o)
+    # Upstream discussion at https://reviews.llvm.org/D150397
+    patchfiles-append 0130-10.14-and-less-availability.patch
+}
+
 post-patch {
     reinplace "s|@@PREFIX@@|${prefix}|" \
         ${patch.dir}/clang/lib/Driver/ToolChains/Clang.cpp \
diff --git a/lang/llvm-18/files/0130-10.14-and-less-availability.patch b/lang/llvm-18/files/0130-10.14-and-less-availability.patch
new file mode 100644
index 0000000000000..6e08aaeffff5f
--- /dev/null
+++ b/lang/llvm-18/files/0130-10.14-and-less-availability.patch
@@ -0,0 +1,40 @@
+This is a conditional revert of https://github.com/llvm/llvm-project/commit/b653a2823fe4b4c9c6d85cfe119f31d8e70c2fa0.
+__attribute__((weak_import)) does not prevent Undefined symbol error.
+
+--- a/compiler-rt/lib/builtins/os_version_check.c.orig	2023-11-28 09:52:28.000000000 +0100
++++ b/compiler-rt/lib/builtins/os_version_check.c	2024-08-29 15:29:18.000000000 +0200
+@@ -13,6 +13,7 @@
+ 
+ #ifdef __APPLE__
+ 
++#include <AvailabilityMacros.h>
+ #include <TargetConditionals.h>
+ #include <dispatch/dispatch.h>
+ #include <dlfcn.h>
+@@ -86,9 +87,11 @@
+                                             CFStringEncoding);
+ typedef void (*CFReleaseFuncTy)(CFTypeRef);
+ 
++#if MAC_OS_X_VERSION_MIN_REQUIRED >= 101500
+ extern __attribute__((weak_import))
+ bool _availability_version_check(uint32_t count,
+                                  dyld_build_version_t versions[]);
++#endif
+ 
+ static void _initializeAvailabilityCheck(bool LoadPlist) {
+   if (AvailabilityVersionCheck && !LoadPlist) {
+@@ -98,8 +101,14 @@
+   }
+ 
+   // Use the new API if it's is available.
++#if MAC_OS_X_VERSION_MIN_REQUIRED >= 101500
+   if (_availability_version_check)
+     AvailabilityVersionCheck = &_availability_version_check;
++#else
++  // __attribute__((weak_import)) does not prevent Undefined symbol error on 10.14
++  AvailabilityVersionCheck = (AvailabilityVersionCheckFuncTy)dlsym(
++      RTLD_DEFAULT, "_availability_version_check");
++#endif
+ 
+   if (AvailabilityVersionCheck && !LoadPlist) {
+     // New API is supported and we're not being asked to load the plist,
diff --git a/lang/llvm-19/Portfile b/lang/llvm-19/Portfile
index a7f811a11ade4..a93140d2fcae6 100644
--- a/lang/llvm-19/Portfile
+++ b/lang/llvm-19/Portfile
@@ -29,7 +29,7 @@ version                 ${llvm_version}.1.6
 name                    llvm-${llvm_version}
 revision                0
 subport                 mlir-${llvm_version}  { revision [ expr ${revision} + 0 ] }
-subport                 clang-${llvm_version} { revision [ expr ${revision} + 0 ] }
+subport                 clang-${llvm_version} { revision [ expr ${revision} + 1 ] }
 subport                 lldb-${llvm_version}  { revision [ expr ${revision} + 0 ] }
 subport                 flang-${llvm_version} { revision [ expr ${revision} + 0 ] }
 
@@ -176,6 +176,16 @@ if {${os.platform} eq "darwin" && ${os.major} <= 16} {
     patchfiles-append 0041-no-Werror-unguarded-availability-new.patch
 }
 
+if {${os.platform} eq "darwin" && ${os.major} < 19} {
+    # https://trac.macports.org/ticket/68522
+    # Undefined symbols for architecture x86_64:
+    #   "__availability_version_check", referenced from:
+    #       ___isPlatformVersionAtLeast in libclang_rt.osx.a(os_version_check.c.o)
+    #       __initializeAvailabilityCheck in libclang_rt.osx.a(os_version_check.c.o)
+    # Upstream discussion at https://reviews.llvm.org/D150397
+    patchfiles-append 0130-10.14-and-less-availability.patch
+}
+
 post-patch {
     reinplace "s|@@PREFIX@@|${prefix}|" \
         ${patch.dir}/clang/lib/Driver/ToolChains/Clang.cpp \
diff --git a/lang/llvm-19/files/0130-10.14-and-less-availability.patch b/lang/llvm-19/files/0130-10.14-and-less-availability.patch
new file mode 100644
index 0000000000000..6e08aaeffff5f
--- /dev/null
+++ b/lang/llvm-19/files/0130-10.14-and-less-availability.patch
@@ -0,0 +1,40 @@
+This is a conditional revert of https://github.com/llvm/llvm-project/commit/b653a2823fe4b4c9c6d85cfe119f31d8e70c2fa0.
+__attribute__((weak_import)) does not prevent Undefined symbol error.
+
+--- a/compiler-rt/lib/builtins/os_version_check.c.orig	2023-11-28 09:52:28.000000000 +0100
++++ b/compiler-rt/lib/builtins/os_version_check.c	2024-08-29 15:29:18.000000000 +0200
+@@ -13,6 +13,7 @@
+ 
+ #ifdef __APPLE__
+ 
++#include <AvailabilityMacros.h>
+ #include <TargetConditionals.h>
+ #include <dispatch/dispatch.h>
+ #include <dlfcn.h>
+@@ -86,9 +87,11 @@
+                                             CFStringEncoding);
+ typedef void (*CFReleaseFuncTy)(CFTypeRef);
+ 
++#if MAC_OS_X_VERSION_MIN_REQUIRED >= 101500
+ extern __attribute__((weak_import))
+ bool _availability_version_check(uint32_t count,
+                                  dyld_build_version_t versions[]);
++#endif
+ 
+ static void _initializeAvailabilityCheck(bool LoadPlist) {
+   if (AvailabilityVersionCheck && !LoadPlist) {
+@@ -98,8 +101,14 @@
+   }
+ 
+   // Use the new API if it's is available.
++#if MAC_OS_X_VERSION_MIN_REQUIRED >= 101500
+   if (_availability_version_check)
+     AvailabilityVersionCheck = &_availability_version_check;
++#else
++  // __attribute__((weak_import)) does not prevent Undefined symbol error on 10.14
++  AvailabilityVersionCheck = (AvailabilityVersionCheckFuncTy)dlsym(
++      RTLD_DEFAULT, "_availability_version_check");
++#endif
+ 
+   if (AvailabilityVersionCheck && !LoadPlist) {
+     // New API is supported and we're not being asked to load the plist,