Automated commit: libchrome r1296734 uprev

Add BUILDFLAGS for raw ptr changes:
 - USE_RAW_PTR_ASAN_UNOWNED_IMPL
 - USE_RAW_PTR_HOOKABLE_IMPL
Add backwards compatibility patch:
  - 0100-File-Stat-Lstat-receive-FilePath-const-char-ptr.patch

Merge with upstream commit 833ae25b9069200b137d77a188bc43ee954a299a

BUG=None
TEST=sudo emerge libchrome

Cq-Depend: chromium:5520277, chrome-internal:7265459
Change-Id: Iad667e8d29cee2736456248f674dce9d73fa9132
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/libchrome/+/5517878
Tested-by: Jae Hoon Kim <kimjae@chromium.org>
Reviewed-by: Grace Cham <hscham@chromium.org>
Commit-Queue: Jae Hoon Kim <kimjae@chromium.org>