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
diff --git a/UPDATING b/UPDATING
index f818987..9703932 100755
--- a/UPDATING
+++ b/UPDATING
@@ -12,6 +12,7 @@
 
 rm -Rf src/.git
 rm -Rf src/fuzz
+rm -Rf src/third_party/googletest
 rm -Rf linux-aarch64/ linux-arm/ linux-x86/ linux-x86_64/ mac-x86/ mac-x86_64/ win-x86_64/ win-x86/
 python src/util/generate_build_files.py android