Separate the build dir and include dir variables

After patching backscrub to install its header into the prefix,
this patch makes obs-backscrub get the header from its installed
location.

The link targets are still fetched from the backscrub build dir
and that variable is renamed to indicate that it is only used
for that purpose.

Both variables can be overridden separately.

See ali1234/backscrub@9dea13b
and phlash#3

CMakeLists.txt

@@ -7,13 +7,16 @@ find_package(LibObs REQUIRED)
 find_package(OpenCV REQUIRED)
 find_package(Threads REQUIRED)
 
-if(NOT DEFINED BACKSCRUB)
-        set(BACKSCRUB ../backscrub)
+if(NOT DEFINED BACKSCRUB_BUILD_DIR)
+        set(BACKSCRUB_BUILD_DIR ../backscrub/build)
+endif()
+
+if (NOT DEFINED LIBBACKSCRUB_INCLUDE_DIR)
+        set(LIBBACKSCRUB_INCLUDE_DIR ${CMAKE_INSTALL_PREFIX}/include)
 endif()
 
 # Pull in backscrub and dependencies
-include(${BACKSCRUB}/build/BackscrubTargets.cmake)
-set(LIBBACKSCRUB_INCLUDE_DIR ${BACKSCRUB})
+include(${BACKSCRUB_BUILD_DIR}/BackscrubTargets.cmake)
 
 set(obs-backscrub_SOURCES
         obs-backscrub.cpp)

obs-backscrub.cpp

@@ -6,7 +6,7 @@
 #include <condition_variable>
 #include <obs-module.h>
 #include <stdio.h>
-#include "lib/libbackscrub.h"
+#include "libbackscrub.h"
 
 // Setting names & default values
 static const char MODEL_SETTING[] = "Segmentation model";