Configure: use a better method to identify gcc and derivates

Looking for 'gcc' and 'clang' in the output from the C compiler is
uncertain.  Some versions report argv[0], which might be /usr/bin/cc
(for example), and others might mention gcc without being gcc or a
derivate.

Better then to fetch predefined macros and checking if __GNUC__ and
__clang__ are defined.

Reviewed-by: Andy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4755)