Add functions to return DH parameters using NID and to return the
NID if parameters match a named set. Currently this supports only
RFC7919 parameters but could be expanded in future.
Reviewed-by: NAndy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4485)

Move the dh_method structure into an internal header file and provide
relevant accessors for the internal fields.
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Now that we have the foundation for the "unified" build scheme in
place, we add build.info files.  They have been generated from the
Makefiles in the same directories.  Things that are platform specific
will appear in later commits.
Reviewed-by: NAndy Polyakov <appro@openssl.org>