clang/gn/win: Stop running the compiler through `ninja -t msvc -e environment.foo`

build/toolchain/win/setup_toolchain.py

Index: build/toolchain/win/setup_toolchain.py
diff --git a/build/toolchain/win/setup_toolchain.py b/build/toolchain/win/setup_toolchain.py
index 1e20387b0b240e987b22e85898c9368d8b0b0b9a..1612b22ca437b60b8fef6dc78aadde1495cae620 100644
--- a/build/toolchain/win/setup_toolchain.py
+++ b/build/toolchain/win/setup_toolchain.py
@@ -126,21 +126,26 @@ def _CopyTool(source_path):
 
 
 def main():
-  if len(sys.argv) != 6:
+  if len(sys.argv) not in (6, 7):
     print('Usage setup_toolchain.py '
           '<visual studio path> <win tool path> <win sdk path> '
-          '<runtime dirs> <target_cpu>')
+          '<runtime dirs> <target_cpu>, <include prefix>')
     sys.exit(2)
   tool_source = sys.argv[2]
   win_sdk_path = sys.argv[3]
   runtime_dirs = sys.argv[4]
   target_cpu = sys.argv[5]
 
+  include_prefix = None
+  if len(sys.argv) > 6:
+    include_prefix = sys.argv[6]
+
   _CopyTool(tool_source)
 
   cpus = ('x86', 'x64')
   assert target_cpu in cpus
   vc_bin_dir = ''
+  include = ''
 
   # TODO(scottmg|goma): Do we need an equivalent of
   # ninja_use_custom_environment_files?
@@ -155,6 +160,9 @@ def main():
         if os.path.exists(os.path.join(path, 'cl.exe')):
           vc_bin_dir = os.path.realpath(path)
           break
+      if include_prefix:
+        include = ' '.join([include_prefix + p
+                            for p in env['INCLUDE'].split(';')])
 
     # The Windows SDK include directories must be first. They both have a sal.h,
     # and the SDK one is newer and the SDK uses some newer features from it not
@@ -179,11 +187,15 @@ def main():
       env['LIBPATH'] = env['LIBPATH'].replace(r'\VC\LIB', r'\VC\LIB\STORE')
     env_block = _FormatAsEnvironmentBlock(env)
     with open('environment.winrt_' + cpu, 'wb') as f:
-        f.write(env_block)
+      f.write(env_block)
 
   assert vc_bin_dir
+  assert '"' not in vc_bin_dir
   print 'vc_bin_dir = "%s"' % vc_bin_dir
-
+  if include_prefix:
+    assert include
+    assert '"' not in include
+    print 'include_flags = "%s"' % include
 
 if __name__ == '__main__':
   main()