Placing FreeBSD-specific stuffs into Diligent-BuildSettings (as requested). This is, in fact, much cleaner than my previous approach. I also placed at the tail of the include directories list so Diligent's headers are prefurred over what's already installed in the system.

Author: LadySerenaKitty

CMakeLists.txt

@@ -204,9 +204,6 @@ elseif(PLATFORM_LINUX)
     set(ARCHIVER_SUPPORTED TRUE CACHE INTERNAL "Archiver is supported on Linux platform")
     if(PLATFORM_FREEBSD)
         target_compile_definitions(Diligent-PublicBuildSettings INTERFACE PLATFORM_LINUX=1 PLATFORM_FREEBSD=1)
-        if(EXISTS /usr/local/include)
-            include_directories(/usr/local/include)
-        endif()
     else()
         target_compile_definitions(Diligent-PublicBuildSettings INTERFACE PLATFORM_LINUX=1)
     endif()
@@ -525,6 +522,9 @@ else()
     set(DILIGENT_INSTALL_PDB OFF)
 endif()
 
+if(PLATFORM_FREEBSD AND EXISTS /usr/local/include)
+	target_include_directories(Diligent-BuildSettings SYSTEM AFTER INTERFACE /usr/local/include)
+endif()
 file(RELATIVE_PATH DILIGENT_CORE_DIR "${CMAKE_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}")
 SET(DILIGENT_CORE_DIR ${DILIGENT_CORE_DIR} CACHE INTERNAL "Diligent Core installation directory")