[clang] Build clang with pinned clang on all platforms

This is a reland of https://crrev.com/c/3590911.

Followup to https://crrev.com/c/3572241.

We can't use NamedTemporaryFile on Windows (can't read from it while having a handle to it): https://docs.python.org/3.9/library/tempfile.html. Use a consistent path for the pinned update.py instead.

Reason for previous revert should be fixed with https://crrev.com/c/3656302.

Bug: 1010466, 1013560
Change-Id: I578ae53afe33c657d48a4c3333e396f2c62eea89
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3656846
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Arthur Eubanks <aeubanks@google.com>
Cr-Commit-Position: refs/heads/main@{#1006103}
NOKEYCHECK=True
GitOrigin-RevId: ad35291af36d609042e1d320adb1568daafef9a8
1 file changed