PNaCl: Update Clang revision in pnacl/COMPONENT_REVISIONS
PNaCl: Update Clang revision in pnacl/COMPONENT_REVISIONS

This pulls in the following Clang change:

a557a57: (dschuff@chromium.org) nacl-clang driver: Use GetLinkerPath utility function to find linker

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4088
TEST= PNaCl toolchain trybots
R=jvoung@chromium.org

Review URL: https://codereview.chromium.org/1179783003.

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client