This reverts commit 6039f821 and reapplies bff6d9bb.
Clang's Index/implicit-attrs.m test invokes c-index-test with -fobjc-arc. This flag is not compatible with -fobjc-runtime=gcc, which gets implied on Linux.
The original commit uncovered this by correctly reporting issues when parsing -cc1 command line.
This commit fixes the test to explicitly provide ObjectiveC runtime compatible with ARC.