Since 91e0d220, the configure checks
about GMP and MPFR for gdb builds have been moved to the toplevel
configure.
However, it doesn't take into account the --disable-gdb option. Meaning
that a build without gdb will require these libraries even if not
needed.

ChangeLog:

	* configure.ac: Skip GMP and MPFR when --disable-gdb is
	provided.
	* configure: Regenerate.