configure: allow --enable-malloc-logging only with glibc

The feature for 'malloc-logging' uses functionalities that are
available only in GNU libc.

Detect in 'configure' if OpenOCD is being compiled with glibc.
Set the macro '_DEBUG_FREE_SPACE_' only in case of glibc.

Change-Id: I43e9b87c7ad47171cfe3e7c1e5f96f11e19f98d0
Signed-off-by: Antonio Borneo <[email protected]>
Reviewed-on: https://review.openocd.org/c/openocd/+/8592
Tested-by: jenkins

configure.ac

@@ -57,6 +57,11 @@ AC_CHECK_TYPE([Elf64_Ehdr],
 	AC_DEFINE([HAVE_ELF64], [1], [Define to 1 if the system has the type 'Elf64_Ehdr'.]),
 	[], [[#include <elf.h>]])
 
+AC_MSG_CHECKING([for glibc])
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <features.h>]], [[int v = __GLIBC__;return 0;]])],
+	[have_glibc=yes], [have_glibc=no])
+AC_MSG_RESULT($have_glibc)
+
 AC_CHECK_HEADERS([fcntl.h])
 AC_CHECK_HEADERS([malloc.h])
 AC_CHECK_HEADERS([netdb.h])
@@ -262,7 +267,7 @@ AC_ARG_ENABLE([malloc_logging],
 
 AC_MSG_CHECKING([whether to enable malloc free space logging]);
 AC_MSG_RESULT([$debug_malloc])
-AS_IF([test "x$debug_malloc" = "xyes"], [
+AS_IF([test "x$debug_malloc" = "xyes" -a "x$have_glibc" = "xyes"], [
   AC_DEFINE([_DEBUG_FREE_SPACE_],[1], [Include malloc free space in logging])
 ])