Roll clang llvmorg-12-init-12923-g6ee22ca6-1 : llvmorg-12-init-15676-g5c951623-1.

Ran `./tools/clang/scripts/upload_revision.py 5c951623bc8965fa1e89660f2f5f4a2944e4981a`.

Bug: 1154382
Change-Id: Iff83fc56e3f0e0172ee4dfdea95cc1144d1d819b
Binary-Size: See analysis in crbug.com/1159421
Cq-Include-Trybots: chromium/try:chromeos-amd64-generic-cfi-thin-lto-rel
Cq-Include-Trybots: chromium/try:dawn-win10-x86-deps-rel
Cq-Include-Trybots: chromium/try:linux-chromeos-dbg
Cq-Include-Trybots: chromium/try:linux_angle_deqp_rel_ng
Cq-Include-Trybots: chromium/try:linux_chromium_cfi_rel_ng
Cq-Include-Trybots: chromium/try:linux_chromium_chromeos_msan_rel_ng
Cq-Include-Trybots: chromium/try:linux_chromium_compile_dbg_32_ng
Cq-Include-Trybots: chromium/try:linux_chromium_msan_rel_ng
Cq-Include-Trybots: chromium/try:mac-arm64-rel,mac_chromium_asan_rel_ng
Cq-Include-Trybots: chromium/try:win-angle-deqp-rel-64
Cq-Include-Trybots: chromium/try:win-asan,win7-rel,win-angle-deqp-rel-32
Cq-Include-Trybots: chrome/try:iphone-device,ipad-device
Cq-Include-Trybots: chrome/try:linux-chromeos-chrome
Cq-Include-Trybots: chrome/try:win-chrome,win64-chrome,mac-chrome
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2605479
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840067}

tools/clang/scripts/update.py

@@ -38,7 +38,7 @@ import zipfile
 # https://chromium.googlesource.com/chromium/src/+/master/docs/updating_clang.md
 # Reverting problematic clang rolls is safe, though.
 # This is the output of `git describe` and is usable as a commit-ish.
-CLANG_REVISION = 'llvmorg-12-init-12923-g6ee22ca6'
+CLANG_REVISION = 'llvmorg-12-init-15676-g5c951623'
 CLANG_SUB_REVISION = 1
 
 PACKAGE_VERSION = '%s-%s' % (CLANG_REVISION, CLANG_SUB_REVISION)