+eugenis who asked about the roll the other day

From crdev: "I am building chromium on Fedora, and it crashes with https://llvm.org/bugs/show_bug.cgi?id=31043. Clang was fixed in r291064."

This will fix libFuzzer Mac compile issue after enabling trace-pc-guard.

r294517 (https://reviews.llvm.org/rL294517) also fixes an important linker problem problem for libfuzzer: 687570

After rolling, we should be able to revert https://codereview.chromium.org/2694053003. (We could also revert https://codereview.chromium.org/2640153006 if we want.)

Any timelines on the roll please! We are choked on two bots.
https://build.chromium.org/p/chromium.fyi/builders/Afl%20Upload%20Linux%20ASan
https://build.chromium.org/p/chromium.lkgr/builders/Win%20ASan%20Release

I gave it a try in https://chromium.googlesource.com/chromium/src/+/c702a811babe12110a84d644ee81b6d99b2f4716 (forgot to put a BUG= line on it). I wouldn't be surprised if it ends up being reverted for some reason though.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b87e5b0b9505543cc4270479af08e60da11cd507

commit b87e5b0b9505543cc4270479af08e60da11cd507
Author: Nico Weber <thakis@chromium.org>
Date: Fri Feb 24 20:25:00 2017

Disable nocompile tests after clang roll

Results need rebasing.

BUG=695991, 685244 
TBR=lazyboy@chromium.org

Review-Url: https://codereview.chromium.org/2711343004 .
Cr-Commit-Position: refs/heads/master@{#452912}

[modify] https://crrev.com/b87e5b0b9505543cc4270479af08e60da11cd507/build/nocompile.gni

we did a follow-up roll in  bug 696607  due to regression in this roll. But mostly it looks like it might stick.