Fix ldbl-128ibm log1pl (-qNaN) spurious "invalid" exception (bug 22693).

The ldbl-128ibm implementation of log1pl does ordered comparisons on a
negative qNaN argument, so resulting in spurious "invalid" exceptions
(for soft-float powerpc; hard-float only avoids this because of GCC
bug 58684 meaning ordered comparison instructions never get
generated).  This patch fixes this by arranging for the test for NaN
or infinity arguments to handle negative arguments as well.

Tested for powerpc (soft float).

	[BZ #22693]
	* sysdeps/ieee754/ldbl-128ibm/s_log1pl.c (__log1pl): Handle
	negative arguments in test for NaN or infinity argument.