This imports part of the fix for CVE-2021-3712, commits
d9d838ddc0ed083fb4c26dd067e71aad7c65ad16,
5f54e57406ca17731b9ade3afd561d3c652e07f2,
23446958685a593d4d9434475734b99138902ed2,
and bb4d2ed4091408404e18b3326e3df67848ef63d0 from upstream. The
others will be imported in follow-up CLs.
Change-Id: Ic35aeb3895935ee94b82a295efade32782e8d1bc
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/49005
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>