Revert of Roll ASan/Win to LLVM r237003 (patchset #1 id:1 of...

Revert of Roll ASan/Win to LLVM r237003 (patchset #1 id:1 of https://codereview.chromium.org/1140623002/)

Reason for revert:
Caused build hangs.
BUG=487929

Original issue's description:
> Roll ASan/Win to LLVM r237003
>
> Brings in coverage support for Windows.
>
> Green build with this revision:
> http://build.chromium.org/p/chromium.fyi/builders/CrWinAsan%20tester/builds/217/steps/gclient%20runhooks/logs/stdio
>
> TBR=inferno@chromium.org
> NOTRY=true
>
> Committed: https://crrev.com/9f05e50063c1c643ecbe7851dc388b6346414c08
> Cr-Commit-Position: refs/heads/master@{#329280}

TBR=rnk@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1134413003

Cr-Commit-Position: refs/heads/master@{#329886}

tools/clang/scripts/update.py

@@ -27,7 +27,7 @@ use_head_revision = ('LLVM_FORCE_HEAD_REVISION' in os.environ or
   not re.search(r'\b(asan)=1', os.environ.get('GYP_DEFINES', '')))
 
 if not use_head_revision:
-  LLVM_WIN_REVISION = '237003'
+  LLVM_WIN_REVISION = '235968'
 
 # Path constants. (All of these should be absolute paths.)
 THIS_DIR = os.path.abspath(os.path.dirname(__file__))