Missing "obj_mac" header file in "dh_lib"

Usage of `NID_undef` symbol without including its definition was causing
a build fail

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/10996)
1 file changed