Always build clang with symbols on Windows

If we always build clang with symbols on Windows then it makes debugging
and profiling easier. The build time costs shouldn't be too bad, and the
generated code will be identical. This would have saved a bit of time in
the investigation of crbug.com/727447.

BUG=727447

Change-Id: Ib065be626db5d6b0b9c27792a0141c5fb696e208
Reviewed-on: https://chromium-review.googlesource.com/572660Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486962}

tools/clang/scripts/update.py

@@ -588,7 +588,7 @@ def UpdateClang(args):
 
   # Build PDBs for archival on Windows.  Don't use RelWithDebInfo since it
   # has different optimization defaults than Release.
-  if sys.platform == 'win32' and args.bootstrap:
+  if sys.platform == 'win32':
     cflags += ['/Zi']
     cxxflags += ['/Zi']
     ldflags += ['/DEBUG', '/OPT:REF', '/OPT:ICF']