configure, libquadmath: Remove unintended AC_CHECK_LIBM [PR111928]

This was a rebase error, that managed to pass testing on Darwin and
Linux (but fails on bare metal).

	PR libquadmath/111928

libquadmath/ChangeLog:

	* Makefile.in: Regenerate.
	* configure: Regenerate.
	* configure.ac: Remove AC_CHECK_LIBM.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>