external/boringssl: Sync to 6d50f475e319de153a43e1dba5a1beca95948c63.

This includes the following changes:

https://boringssl.googlesource.com/boringssl/+log/0726fb76ebe7f422e3c4fb2e25a0064926975770..6d50f475e319de153a43e1dba5a1beca95948c63

This also updates the build files to add the new GTest-based targets and
work with the C++ file in libssl.

Test: cts-tradefed run cts -m CtsLibcoreOkHttpTestCases -a arm64-v8a
Test: cts-tradefed run cts -m CtsLibcoreTestCases -a arm64-v8a

Change-Id: I99718d51c901fe2e2e1e0398fc61fe1e76ccdb3f
60 files changed