Revert of Build the IRT with nacl-clang for x86

Revert of Build the IRT with nacl-clang for x86 (patchset #16 id:290001 of https://codereview.chromium.org/940993003/)

Reason for revert:
F%*$^ windows XP

Original issue's description:
> Build the IRT with nacl-clang for x86
> 
> This should result in faster builds, and in the future could
> allow cleanups of the IRT-building gyp code and the PNaCl drivers.
> 
> * Use -mstackrealign and -mno-sse to be callable with under-aligned stacks.
> * Use -integrated-as to ensure sandbox base address hiding on x86-64.
> * Uses -fno-exceptions to reduce the size, and links with
>   PNaCl's unwind stubs to avoid including the unwinder (which
>   would otherwise be pulled in by libcxx).
> * Remove -gline-tables-only which was a workaround for
>   slowness and excessive memory consumption in bitcode linking
> * Also use nacl-clang for the SCons core IRT build.
> 
> BUG= https://code.google.com/p/nativeclient/issues/detail?id=4088
> R=jvoung@chromium.org, mseaborn@chromium.org
> 
> Committed: https://chromium.googlesource.com/native_client/src/native_client/+/316f3e53bfcc34e4a137abbce02d890e3ea968ce

TBR=jvoung@chromium.org,mseaborn@chromium.org,mcgrathr@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG= https://code.google.com/p/nativeclient/issues/detail?id=4088

Committed: https://chromium.googlesource.com/native_client/src/native_client/+/70e1707b52d1740660479fc7e83cf250445cb6e1

[Derek Schuff, 2015-03-25 22:45:22]

Created Revert of Build the IRT with nacl-clang for x86

[commit-bot: I haz the power, 2015-03-25 22:45:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1036513005/1

[commit-bot: I haz the power, 2015-03-25 22:46:00]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/native_client/src/native_client/+/70e1707b5...