external/boringssl: sync with upstream.

See the following URL for a list of the changes included in this sync:

https://boringssl.googlesource.com/boringssl/+log/d98dc1311e20193ac188e359e91aeaaf5cc3a7e2..51a01a5cd44b3bdfab5220847000f13fc85f000b

Change-Id: I36535827f652536dfd687c1646bbea1535fc8e44
224 files changed