Rename a number of BUF_* functions to OPENSSL_*.

Upstream did this in 7644a9aef8932ed4d1c3f25ed776c997702982be, so align
with them. Add the new OPENSSL_* names and switch all callers witihn the
library to match. Keep the old BUF_* names around for compatibility.

Note there were two functions where we already had an OPENSSL_* version:
OPENSSL_strdup and OPENSSL_strnlen. The former now gains a NULL check to
align with BUF_strdup. The latter gets deduplicated; we had two
implementations.

Change-Id: Ia1cd4527a752fcd62e142ed1e1d7768d323279ba
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/38425
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

ssl/ssl_lib.cc

diff --git a/ssl/ssl_lib.cc b/ssl/ssl_lib.cc
index 703c2bc..a53a5e3 100644
--- a/ssl/ssl_lib.cc
+++ b/ssl/ssl_lib.cc
@@ -699,7 +699,7 @@
 
   if (ctx->psk_identity_hint) {
     ssl->config->psk_identity_hint.reset(
-        BUF_strdup(ctx->psk_identity_hint.get()));
+        OPENSSL_strdup(ctx->psk_identity_hint.get()));
     if (ssl->config->psk_identity_hint == nullptr) {
       return nullptr;
     }
@@ -2129,7 +2129,7 @@
     OPENSSL_PUT_ERROR(SSL, SSL_R_SSL3_EXT_INVALID_SERVERNAME);
     return 0;
   }
-  ssl->hostname.reset(BUF_strdup(name));
+  ssl->hostname.reset(OPENSSL_strdup(name));
   if (ssl->hostname == nullptr) {
     OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
     return 0;
@@ -2580,7 +2580,7 @@
   // ECDHE_PSK can only spell empty hint. Having different capabilities is odd,
   // so we interpret empty and missing as identical.
   if (identity_hint != NULL && identity_hint[0] != '\0') {
-    out->reset(BUF_strdup(identity_hint));
+    out->reset(OPENSSL_strdup(identity_hint));
     if (*out == nullptr) {
       return 0;
     }