Reland "Roll clang 340925:342523."

This reverts commit f6a8902e.

Reason for revert: relanding with lto for android disabled until
things are sorted out.

Original change's description:
> Revert "Roll clang 340925:342523."
> 
> This reverts commit 34893e97.
> 
> Reason for revert: New failures on Android in computeKnownBits(), looks like an LTO problem. http://crbug.com/887272
> 
> Original change's description:
> > Roll clang 340925:342523.
> > 
> > Ran `tools/clang/scripts/upload_revision.py 342523`.
> > 
> > Bug: 880827
> > Change-Id: I8f747ab4a2de74a0f0b4b5a201d37e111f323077
> > Reviewed-on: https://chromium-review.googlesource.com/1232590
> > Reviewed-by: Reid Kleckner <rnk@chromium.org>
> > Commit-Queue: Nico Weber <thakis@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#592531}
> 
> TBR=thakis@chromium.org,hans@chromium.org,rnk@chromium.org
> 
> Change-Id: Idee414178ab15058aa080f670585cee81e0f8ac5
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 880827
> Reviewed-on: https://chromium-review.googlesource.com/1236003
> Reviewed-by: Egor Pasko <pasko@chromium.org>
> Commit-Queue: Egor Pasko <pasko@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#592765}

TBR=pasko@chromium.org,thakis@chromium.org,hans@chromium.org,rnk@chromium.org

Change-Id: I26ea97e83cfebcec0670e79683fe0db7f993c1a7
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 880827
Reviewed-on: https://chromium-review.googlesource.com/1236174
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592778}

build/config/compiler/compiler.gni

@@ -48,7 +48,8 @@ declare_args() {
 
   # Enables support for ThinLTO, which links 3x-10x faster than full LTO. See
   # also http://blog.llvm.org/2016/06/thinlto-scalable-and-incremental-lto.html
-  use_thin_lto = is_cfi || (is_android && is_official_build)
+  # TODO(https://crbug.com/887272): Reenable on is_android && is_official_build
+  use_thin_lto = is_cfi
 
   # Tell VS to create a PDB that references information in .obj files rather
   # than copying it all. This should improve linker performance. mspdbcmf.exe

tools/clang/scripts/update.py

@@ -27,7 +27,7 @@ import zipfile
 # Do NOT CHANGE this if you don't know what you're doing -- see
 # https://chromium.googlesource.com/chromium/src/+/master/docs/updating_clang.md
 # Reverting problematic clang rolls is safe, though.
-CLANG_REVISION = '340925'
+CLANG_REVISION = '342523'
 
 use_head_revision = bool(os.environ.get('LLVM_FORCE_HEAD_REVISION', '0')
                          in ('1', 'YES'))
@@ -35,7 +35,7 @@ if use_head_revision:
   CLANG_REVISION = 'HEAD'
 
 # This is incremented when pushing a new build of Clang at the same revision.
-CLANG_SUB_REVISION=2
+CLANG_SUB_REVISION=1
 
 PACKAGE_VERSION = "%s-%s" % (CLANG_REVISION, CLANG_SUB_REVISION)