Makefile: Exclude dummy header asn1_mac.h from CRYPTOHEADERS

Reviewed-by: NPaul Dale <pauli@openssl.org>
Reviewed-by: NTomas Mraz <tomas@openssl.org>
Reviewed-by: NDavid von Oheimb <david.von.oheimb@siemens.com>
(Merged from https://github.com/openssl/openssl/pull/15913)

Configurations/unix-Makefile.tmpl

@@ -1274,7 +1274,8 @@ errors:
            include/internal/asn1.h
            include/internal/sslconf.h );
    my @cryptoskipheaders = ( @sslheaders_tmpl,
-       qw( include/openssl/conf_api.h
+       qw( include/openssl/asn1_mac.h
+           include/openssl/conf_api.h
            include/openssl/ebcdic.h
            include/openssl/opensslconf.h
            include/openssl/symhacks.h ) );