Fix powerpc-nofpu complex long double functions spurious "invalid" exception (bug 22687).

For soft-float powerpc, various _Complex long double functions
generate spurious "invalid" exceptions, even with a compiler with GCC
bug 64811 fixed.

The problem is GCC's built-in fabsl expansion.  Various files are
already built with -fno-builtin-fabsl because in this case (IBM long
double, for soft-float or e500v1) a fallback fabsl expansion based on
comparisons is used, which can produce the wrong sign of a zero
result.  Those comparisons can also produce spurious exceptions for
NaN arguments.  Furthermore, __builtin_fpclassify implemently uses
__builtin_fabsl, and is unaffected by -fno-builtin-fabsl, and the
fpclassify macro uses __builtin_fpclassify in the absence of
-fsignaling-nans.  Thus, this patch arranges for the problem files
using fpclassify to be built with -fsignaling-nans in this case, to
avoid spurious exceptions from fpclassify.

Tested for powerpc (soft-float).

	[BZ #22687]
	* sysdeps/powerpc/nofpu/Makefile (CFLAGS-s_cacosl.c): New
	variable.
	(CFLAGS-s_cacoshl.c): Likewise.
	(CFLAGS-s_casinhl.c): Likewise.
	(CFLAGS-s_catanl.c): Likewise.
	(CFLAGS-s_catanhl.c): Likewise.
	(CFLAGS-s_cexpl.c): Likewise.
	(CFLAGS-s_ccoshl.c): Add -fsignaling-nans.
	(CFLAGS-s_csinhl.c): Likewise.
	(CFLAGS-s_clogl.c): Likewise.
	(CFLAGS-s_clog10l.c): Likewise.
	(CFLAGS-s_csinl.c): Likewise.
	(CFLAGS-s_csqrtl.c): Likewise.