Revert "android: Disable thinLTO for 32-bit ARM builds."

This reverts commit 069a1be1.

Reason for revert: Clang roll with the upstream bug fix has landed.

Original change's description:
> android: Disable thinLTO for 32-bit ARM builds.
> 
> This is done to avoid a runtime crash at startup when
> Chrome starts up on devices with a very old Linux kernel.
> 
> This is only one way to address the problem, but probably
> the simplest patch to fix it. See bug entry for all details
> and alternatives considered.
> 
> BUG=871722
> R=​agrieve@chromium.org, pcc@chromium.org, thakis@chromium.org
> 
> Change-Id: I9a197a347538ae9cf9ce6de7b243f522cb425043
> Reviewed-on: https://chromium-review.googlesource.com/1167502
> Reviewed-by: Peter Collingbourne <pcc@chromium.org>
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Commit-Queue: David Turner <digit@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#581627}

TBR=digit@chromium.org,thakis@chromium.org,pcc@chromium.org,agrieve@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 871722, 872611
Change-Id: I02d8b5519b978fd61b8cd2ead8718ff77846b402
Reviewed-on: https://chromium-review.googlesource.com/1199937Reviewed-by: Peter Collingbourne <pcc@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Peter Collingbourne <pcc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588189}

build/config/compiler/compiler.gni

@@ -43,10 +43,7 @@ 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
-  # NOTE: See http://crbug.com/871722 to understand why this is disabled for
-  # 32-bit Android/ARM
-  use_thin_lto =
-      is_cfi || (is_android && is_official_build && target_cpu != "arm")
+  use_thin_lto = is_cfi || (is_android && is_official_build)
 
   # Tell VS to create a PDB that references information in .obj files rather
   # than copying it all. This should improve linker performance. mspdbcmf.exe