Add misc functions for easier porting.

Android requested that the wpa_supplicant go upstream. This change adds
some dummy functions and reinstates DSA_dup_DH in order to make the diff
smaller and easier for upstream.

Change-Id: I77ac271b8652bae5a0bbe16afde51d9096f3dfb5
Reviewed-on: https://boringssl-review.googlesource.com/1740
Reviewed-by: Adam Langley <agl@google.com>