libclc: Fix building against an llvm build directory

Reviewed By: thieta

Differential Revision: https://reviews.llvm.org/D142718

(cherry picked from commit 8040e3a)

libclc/CMakeLists.txt

@@ -105,7 +105,10 @@ endif()
 
 enable_language( CLC LLAsm )
 # This needs to be set before any target that needs it
-include_directories( ${LLVM_INCLUDE_DIR} )
+# We need to use LLVM_INCLUDE_DIRS here, because if we are linking to an
+# llvm build directory, this includes $src/llvm/include which is where all the
+# headers are not $build/include/ which is what LLVM_INCLUDE_DIR is set to.
+include_directories( ${LLVM_INCLUDE_DIRS} )
 
 # Setup prepare_builtins tools
 set(LLVM_LINK_COMPONENTS