[GN]: Add asmflags

+ Also, don’t specify a PCH as a dependency for a build rule that doesn't support PCH.

BUG=418613

Review URL: https://codereview.chromium.org/1361173004

Cr-Original-Commit-Position: refs/heads/master@{#350654}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 40fc4844e1a0dd91378044911fd2df573447369d
13 files changed
tree: 79eb2d8921e3e9a3227280faced4be14ff1bf30f
  1. tools/