external/boringssl: Sync to 0e9138d2.

This includes the following changes:

https://boringssl.googlesource.com/boringssl/+log/aa24851515d6280aa1d6a8b1548fe74691df3136..0e9138d295cd556e830dc8b3be735e808680f4bd

This requires some build tweaks:

- trusty's rules.mk builds with BORINGSSL_NO_CXX to suppress the new C++
  scopers since they build their version of keymaster without the STL.

- BORINGSSL_ENABLE_RC4_TLS to temporarily keep RC4 in the TLS stack.

Change-Id: Ic688ec5779f649a4912b00fb2b55cba64fb07449
diff --git a/src/include/openssl/buf.h b/src/include/openssl/buf.h
index 8ae856b..30f3af7 100644
--- a/src/include/openssl/buf.h
+++ b/src/include/openssl/buf.h
@@ -117,6 +117,17 @@
 
 #if defined(__cplusplus)
 }  /* extern C */
+
+extern "C++" {
+
+namespace bssl {
+
+BORINGSSL_MAKE_DELETER(BUF_MEM, BUF_MEM_free)
+
+}  // namespace bssl
+
+}  /* extern C++ */
+
 #endif
 
 #endif  /* OPENSSL_HEADER_BUFFER_H */