Adjust bfd/warning.m4 egrep patterns

Adjust bfd/warning.m4 egrep patterns

Adjust the `bfd/warning.m4` `egrep` patterns to handle preprocessors
that do not define `__GNUC__`, leaving the string in the output.

bfd/
	* warning.m4: Adjust egrep pattern for non-GNU compilers.
	* configure: Regenerate.
binutils/
	* configure: Regenerate.
gas/
	* configure: Regenerate.
gold/
	* configure: Regenerate.
gprof/
	* configure: Regenerate.
ld/
	* configure: Regenerate.
opcodes/
	* configure: Regenerate.