win: Decide how to include system dirs at toolchain time instead of globally.

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 43a7e09adf3b3988198570dfdad4285fa0b791f4..ec60564070c118bfcf4d0d9e50c295c3e8a4e94e 100644
--- a/build/toolchain/win/setup_toolchain.py
+++ b/build/toolchain/win/setup_toolchain.py
@@ -152,7 +152,7 @@ def _FormatAsEnvironmentBlock(envvar_dict):
 
 
 def main():
-  if len(sys.argv) != 6:
+  if len(sys.argv) != 5:
     print('Usage setup_toolchain.py '
           '<visual studio path> <win sdk path> '
           '<runtime dirs> <target_cpu> <include prefix>')
@@ -160,7 +160,6 @@ def main():
   win_sdk_path = sys.argv[2]
   runtime_dirs = sys.argv[3]
   target_cpu = sys.argv[4]
-  include_prefix = sys.argv[5]
 
   cpus = ('x86', 'x64')
   assert target_cpu in cpus
@@ -182,8 +181,9 @@ def main():
           break
       # The separator for INCLUDE here must match the one used in
       # _LoadToolchainEnv() above.
-      include = [include_prefix + p for p in env['INCLUDE'].split(';') if p]
-      include = ' '.join(['"' + i.replace('"', r'\"') + '"' for i in include])
+      include = [p.replace('"', r'\"') for p in env['INCLUDE'].split(';') if p]
+      include_I = ' '.join(['"/I' + i + '"' for i in include])
+      include_imsvc = ' '.join(['"-imsvc' + i + '"' for i in include])
 
     env_block = _FormatAsEnvironmentBlock(env)
     with open('environment.' + cpu, 'wb') as f:
@@ -200,8 +200,10 @@ def main():
 
   assert vc_bin_dir
   print 'vc_bin_dir = ' + gn_helpers.ToGNString(vc_bin_dir)
-  assert include
-  print 'include_flags = ' + gn_helpers.ToGNString(include)
+  assert include_I
+  print 'include_flags_I = ' + gn_helpers.ToGNString(include_I)

[Nico, 2017/03/03 22:17:48]

this is currently not read anywhere, but if the MS branch where to use this flag
instead of the env subprocess, this is how we'd do it. seemed a bit nicer to
output this too, but I can drop include_I if you think YAGNI is better. (I
usually do think that.)

+  assert include_imsvc
+  print 'include_flags_imsvc = ' + gn_helpers.ToGNString(include_imsvc)
 
 if __name__ == '__main__':
   main()