Use ';' as the path separator in setup_toolchain.py on Windows cross build

On cross build of Windows Chrome on Linux, path detections in
setup_toolchain.py fail due to path separator mismatch.

https://chromium-review.googlesource.com/c/chromium/src/+/923161
broke the win/cross build, this fixes it.

Bug: 495204
Change-Id: I1fe5405ce956b8e7522958704c012000df42966e
Reviewed-on: https://chromium-review.googlesource.com/980392
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#545784}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 1337ce842367e0bd9aec9d919d2e7c08592a0daa

toolchain/win/setup_toolchain.py

@@ -211,17 +211,17 @@ def main():
           vc_bin_dir = os.path.realpath(path)
           break
 
-      for path in env['LIB'].split(os.pathsep):
+      for path in env['LIB'].split(';'):
         if os.path.exists(os.path.join(path, 'msvcrt.lib')):
           vc_lib_path = os.path.realpath(path)
           break
 
-      for path in env['LIB'].split(os.pathsep):
+      for path in env['LIB'].split(';'):
         if os.path.exists(os.path.join(path, 'atls.lib')):
           vc_lib_atlmfc_path = os.path.realpath(path)
           break
 
-      for path in env['LIB'].split(os.pathsep):
+      for path in env['LIB'].split(';'):
         if os.path.exists(os.path.join(path, 'User32.Lib')):
           vc_lib_um_path = os.path.realpath(path)
           break