Set CC.host and CXX.host to clang as well on the clang bots.

build/scripts/slave/compile.py

 #!/usr/bin/python
 # Copyright (c) 2011 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """A tool to build chrome, executed by buildbot.
 
   When this is run, the current directory (cwd) should be the outer build
   directory (e.g., chrome-release/build/).
 
@@ skipping 223 matching lines @@
     goma_jobs = 100
     if jobs < goma_jobs:
       jobs = goma_jobs
     command.append('-j%d' % jobs)
     return
 
   if compiler == 'clang':
     clang_dir = os.path.abspath(os.path.join(
         slave_utils.SlaveBaseDir(options.build_dir), 'build', 'src',
         'third_party', 'llvm-build', 'Release+Asserts', 'bin'))
-    env['CC'] = os.path.join(clang_dir, 'clang')
-    env['CXX'] = os.path.join(clang_dir, 'clang++')
+    env['CC.host'] = env['CC'] = os.path.join(clang_dir, 'clang')
+    env['CXX.host'] = env['CXX'] = os.path.join(clang_dir, 'clang++')
 
     # We intentionally don't reuse the ccache/distcc modifications,
     # as they don't work with clang.
     command.append('-j%d' % jobs)
     command.append('-r')
     return
 
   # Use gcc and g++ by default.
   cc = 'gcc'
   cpp = 'g++'
@@ skipping 441 matching lines @@
     main = build_tool_map.get(options.build_tool)
     if not main:
       sys.stderr.write('Unknown build tool %s.\n' % repr(options.build_tool))
       return 2
 
   return main(options, args)
 
 
 if '__main__' == __name__:
   sys.exit(real_main())