Linux GN: support override of clang to different path
Linux GN: support override of clang to different path

Goes with
https://chromium-review.googlesource.com/c/crashpad/crashpad/+/935470.

Bug: crashpad:79, crashpad:220
Change-Id: I5b1c99d526b698422a85eae2ad5b53673b0278a3
Reviewed-on: https://chromium-review.googlesource.com/935469
Reviewed-by: Mark Mentovai <f1b5a91d4d6ad523f2610114591c007e75d15084@chromium.org>

chromium/mini_chromium,chromium/mini_chromium,chromium/mini_chromium