Replace Scoped* heap types with bssl::UniquePtr.

Unlike the Scoped* types, bssl::UniquePtr is available to C++ users, and
offered for a large variety of types.  The 'extern "C++"' trick is used
to make the C++ bits digestible to C callers that wrap header files in
'extern "C"'.

Change-Id: Ifbca4c2997d6628e33028c7d7620c72aff0f862e
Reviewed-on: https://boringssl-review.googlesource.com/10521
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/include/openssl/rsa.h b/include/openssl/rsa.h
index b4c7653..f761dc6 100644
--- a/include/openssl/rsa.h
+++ b/include/openssl/rsa.h
@@ -636,6 +636,21 @@
 
 #if defined(__cplusplus)
 }  /* extern C */
+
+extern "C++" {
+
+namespace bssl {
+
+namespace internal {
+
+BORINGSSL_MAKE_DELETER(RSA, RSA_free)
+
+}  // namespace internal
+
+}  // namespace bssl
+
+}  /* extern C++ */
+
 #endif
 
 #define RSA_R_BAD_ENCODING 100