clang upload.sh: don't download Clang binaries from clang_upload bots.

tools/clang/scripts/update.py

Index: tools/clang/scripts/update.py
diff --git a/tools/clang/scripts/update.py b/tools/clang/scripts/update.py
index b1a59b7405401d56026d81e81ba052b906200935..8b922b831a0c234db5c0a07b8f03dcc968dcbc85 100755
--- a/tools/clang/scripts/update.py
+++ b/tools/clang/scripts/update.py
@@ -722,6 +722,11 @@ def main():
 
   if args.if_needed:
     is_clang_required = False
+    # We don't need to download the toolchain on upload bots during runhooks.
+    if 'LLVM_FORCE_LOCAL_BUILD' in os.environ:
+      print ('Skipping downloading Clang toolchain binaries as '
+             'LLVM_FORCE_LOCAL_BUILD is found in the environment')

[Nico, 2016/03/05 00:11:12]

doesn't this mean the tot bots will stop building clang since they now exit
here?

[krasin1, 2016/03/05 04:43:00]

ToT bots use LLVM_FORCE_HEAD_REVISION. And LLVM_FORCE_LOCAL_BUILD is not
currently used.

+      return 0
     # clang is always used on Mac and Linux.
     if sys.platform == 'darwin' or sys.platform.startswith('linux'):
       is_clang_required = True