Tools: Disable clangrefactoringbackend again

The plugin is disabled and the backend causes compile issues
with older gcc.

Change-Id: I6c809d397872a77168ae4f51d01e9e4f5af3b64f
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/tools/tools.pro

@@ -21,7 +21,7 @@ mac {
 isEmpty(LLVM_INSTALL_DIR):LLVM_INSTALL_DIR=$$(LLVM_INSTALL_DIR)
 exists($$LLVM_INSTALL_DIR) {
     SUBDIRS += clangbackend
-    SUBDIRS += clangrefactoringbackend
+#    SUBDIRS += clangrefactoringbackend
 }
 
 isEmpty(BUILD_CPLUSPLUS_TOOLS):BUILD_CPLUSPLUS_TOOLS=$$(BUILD_CPLUSPLUS_TOOLS)