add -Wold-style-definition

add -Wold-style-definition

This adds -Wold-style-definition to gdb's list of warnings.  This
found a couple of spots where "()" was used where "(void)" is more
correct.

Tested by rebuilding on x86-64 Fedora 18.

	* configure.ac (build_warnings): Add -Wold-style-definition.
	* configure: Rebuild.
	* machoread.c (_initialize_machoread): Use "(void)".
	* macrocmd.c (macro_inform_no_debuginfo): Fix formatting;
	use "(void)".