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

This pulls in the following LLVM changes:

7acbb4c: (jfb@chromium.org) PNaCl: Rewrite @llvm.assume calls to nothing.
bf706a5: (jfb@chromium.org) PNaCl: Strip `nonnull` attributes from pointer arguments.

TEST= PNaCl toolchain trybots
TBR= dschuff@chromium.org

Review URL: https://codereview.chromium.org/1041023002

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