llvm_tools: add a lexan crash autouploader

This CL adds an autouploader for crashes that land in Lexan's bucket.
This autouploader uploads them to 4c, much like how
`bisect_clang_crashes.py` does. The intent is to run this regularly on
chrotomation.

BUG=None
TEST=Ran it

Change-Id: I7cfbe463d89994f6ed3f750c9e8277e1fad0738e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/2451306
Reviewed-by: Jian Cai <jiancai@google.com>
Tested-by: George Burgess <gbiv@chromium.org>
3 files changed