Fold stack-allocated types into headers.

Now that we have the extern "C++" trick, we can just embed them in the
normal headers. Move the EVP_CIPHER_CTX deleter to cipher.h and, in
doing so, take away a little bit of boilerplate in defining deleters.

Change-Id: I4a4b8d0db5274a3607914d94e76a38996bd611ec
Reviewed-on: https://boringssl-review.googlesource.com/10804
Reviewed-by: Matt Braithwaite <mab@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/hmac.h b/include/openssl/hmac.h
index 35c7f58..e4cc04e 100644
--- a/include/openssl/hmac.h
+++ b/include/openssl/hmac.h
@@ -155,6 +155,20 @@
 
 #if defined(__cplusplus)
 }  /* extern C */
+
+#if !defined(BORINGSSL_NO_CXX)
+extern "C++" {
+
+namespace bssl {
+
+using ScopedHMAC_CTX =
+    internal::StackAllocated<HMAC_CTX, void, HMAC_CTX_init, HMAC_CTX_cleanup>;
+
+}  // namespace bssl
+
+}  // extern C++
+#endif
+
 #endif
 
 #endif  /* OPENSSL_HEADER_HMAC_H */