Fix i386/x86_64 log10l (sNaN) (bug 20228).

Fix i386/x86_64 log10l (sNaN) (bug 20228).

The i386/x86_64 versions of log10l return sNaN for sNaN input.  This
patch fixes them to add a NaN input to itself so that qNaN is returned
in this case.

Tested for x86_64 and x86.

	[BZ #20228]
	* sysdeps/i386/fpu/e_log10l.S (__ieee754_log10l): Add NaN input to
	itself.
	* sysdeps/x86_64/fpu/e_log10l.S (__ieee754_log10l): Likewise.
	* math/libm-test.inc (log10_test_data): Add sNaN tests.