setup_links.py fix so that FFmpeg compiles on windows.

Fix creates a symlink tools/generate_stubs -> chromium/src/tools/generate_stubs which is used by ffmpeg on windows.

BUG=468365
NOTRY=True

Review URL: https://codereview.webrtc.org/1586083003

Cr-Commit-Position: refs/heads/master@{#11264}

setup_links.py

@@ -66,6 +66,7 @@ DIRECTORIES = [
   'third_party/zlib',
   'tools/clang',
   'tools/generate_library_loader',
+  'tools/generate_stubs',
   'tools/gn',
   'tools/gyp',
   'tools/memory',