external/boringssl: Sync to ab20cec1c1de815de8da6cc74c2503460efd6e1c.

This includes the following changes:

https://boringssl.googlesource.com/boringssl/+log/b2ff2623a88a65fd4db42d3820f3d8c64e8ab180..ab20cec1c1de815de8da6cc74c2503460efd6e1c

Change-Id: I68612cda7addda1a39f13abcee78c39ebb0ee361
Test: Libcore CTS presubmit
16 files changed