Fix compilation issues with objc modules

Summary:It turns out, apple clang turns off cxx-modules under the hood. Open source clang doesn't do it by default
and we need to do it ourselves.

Reviewed By: jvillard, martinoluca

Differential Revision: D3201604

fb-gh-sync-id: 82cea0f
fbshipit-source-id: 82cea0f

infer/lib/xcode_wrappers/clang

@@ -18,4 +18,4 @@ if [ -z "$INFER_RESULTS_DIR" ]; then
 fi
 
 
-"${CLANG_WRAPPERS_PATH%/}/clang_general_wrapper$XX" "$@"
+"${CLANG_WRAPPERS_PATH%/}/clang_general_wrapper$XX" "$@" -fno-cxx-modules