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

This pulls in the following LLVM change:

a658447: (kschimpf@google.com) Fix the block stack used by the bitstream cursor.

BUG=none
TEST= PNaCl toolchain trybots

Review URL: https://codereview.chromium.org/1820893004

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