external/boringssl: Sync to d18cb77.

This includes the following changes which are far too many to list here:

https://boringssl.googlesource.com/boringssl/+log/7b8b9c17db93ea5287575b437c77fb36eeb81b31..d18cb77864dcc4b5c7cb08c2331008c01165f34f

This also retires one function from android_compat_hacks.c which is no longer
necessary.

Change-Id: Ie00536d7ad815464b2b031f7bcd1b683e12c1623
diff --git a/src/include/openssl/buf.h b/src/include/openssl/buf.h
index 76e3795..f4e315c 100644
--- a/src/include/openssl/buf.h
+++ b/src/include/openssl/buf.h
@@ -67,7 +67,7 @@
 /* Memory and string functions, see also mem.h. */
 
 
-/* BUF_MEM is a generic buffer object used by OpenSSL. */
+/* buf_mem_st (aka |BUF_MEM|) is a generic buffer object used by OpenSSL. */
 struct buf_mem_st {
   size_t length; /* current number of bytes */
   char *data;