Revert of Remove old/unused atomicops code

Revert of Remove old/unused atomicops code (patchset #7 id:140001 of https://codereview.chromium.org/1211903003/)

Reason for revert:
Temporarily reverting until libc++ ships to stable on Android.

Original issue's description:
> Remove old/unused atomicops code
> 
> None of these gcc versions of atomicopts are used in
> chromium anymore.  The portable versions were added in:
> https://codereview.chromium.org/636783002 and all our
> GCC-based targets use those now.
> 
> This change mostly just removes dead code.
> 
> Some files were added to base/allocator/BUILD.gn in order
> to have it match allocator.gyp.   These were not required
> before but are now (specifically tcmalloc's
> base/atomicops-internals-x86.cc).  We got away without it
> previously since base/atomicops_internals_x86_gcc.cc
> provided the same symbol, but the symbol collision was
> arguably a bug.
> 
> BUG=423074
> 
> Committed: https://crrev.com/b030801fcf447602931b3e4b8f94aae8053c61fb
> Cr-Commit-Position: refs/heads/master@{#337123}

TBR=jfb@chromium.org,rmcilroy@chromium.org,danalbert@google.com,thakis@chromium.org,sbc@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=423074, 487341, 427718

[jdduke (slow), 2015-07-21 21:11:18]

Created Revert of Remove old/unused atomicops code

[jdduke (slow), 2015-07-21 21:15:44]

Preparing this revert should we need it to get M45 beta working on x86_64.

[JF, 2015-07-21 21:20:16]

Could you clarify which version of libc++ is broken and how? It would be good to
know when this patch can be reapplied.

[jdduke (slow), 2015-07-21 21:24:45]

On 2015/07/21 21:20:16, JF wrote:
> Could you clarify which version of libc++ is broken and how? It would be good
to
> know when this patch can be reapplied.

See crbug.com/487341 for details. In particular, we're finding that there are
some rendering issues with x86_64 builds on Intel GPUs. We still don't know what
exactly is broken, let alone why or whether the "fault" lies with us or their
driver.