Add clang patch with OpenCL 3.0 feature macro support

Author: azabazno

CMakeLists.txt

@@ -81,8 +81,10 @@ if(NOT USE_PREBUILT_LLVM)
 
     if(NOT LLVM_EXTERNAL_CLANG_SOURCE_DIR)
         set(CLANG_SOURCE_DIR ${LLVM_SOURCE_DIR}/tools/clang)
+        set(CLANG_BASE_REVISION origin/release_10)
     elseif(EXISTS "${LLVM_EXTERNAL_CLANG_SOURCE_DIR}/CMakeLists.txt")
         set(CLANG_SOURCE_DIR "${LLVM_EXTERNAL_CLANG_SOURCE_DIR}")
+        set(CLANG_BASE_REVISION origin/release/10.x)
     endif()
     if(EXISTS ${CLANG_SOURCE_DIR})
         message(STATUS "Using Clang source code direcotry: ${CLANG_SOURCE_DIR}")
@@ -117,7 +119,6 @@ if(NOT USE_PREBUILT_LLVM)
         )
     endif()
 
-    set(CLANG_BASE_REVISION master)
     set(SPIRV_BASE_REVISION master)
     set(TARGET_BRANCH "ocl-open-100")