CMakeLists.txt: Fix issue with rocrtst

Fix for issue where rocrtst could not be built if out directory 
was outside the src (WORK_ROOT) directory due to hard-coded 
relative path for OPENCL_INC_DIR.

Change-Id: Icb93de2266d568e9c2437166e34c88ec526fb45c

rocrtst/suites/test_common/CMakeLists.txt

@@ -97,7 +97,11 @@ else()
 endif()
 
 if(NOT EXISTS "${OPENCL_INC_DIR}/opencl-c.h")
-  set(OPENCL_INC_DIR "${OPENCL_DIR}/../../../external/llvm-project/clang/lib/Headers/")
+  if(DEFINED ENV{WORK_ROOT})
+    set(OPENCL_INC_DIR "$ENV{WORK_ROOT}/external/llvm-project/clang/lib/Headers/")
+  else()
+    set(OPENCL_INC_DIR "${OPENCL_DIR}/../../../external/llvm-project/clang/lib/Headers/")
+  endif()
   if(NOT EXISTS "${OPENCL_INC_DIR}/opencl-c.h")
     message(WARNING "opencl-c.h not found.")
   endif()