Commit a6a4395d fixed modf implementation by compiling s_modf.c and
s_modff.c with -fsignaling-nans. However these files are also included
from the pre-POWER5+ implementation, and thus these files should also
be compiled with -fsignaling-nans.
Changelog:
[BZ #20240]
* sysdeps/powerpc/powerpc32/power4/fpu/multiarch/Makefile
(CFLAGS-s_modf-ppc32.c): New variable.
(CFLAGS-s_modff-ppc32.c): Likewise.
* sysdeps/powerpc/powerpc64/fpu/multiarch/Makefile
(CFLAGS-s_modf-ppc64.c): Likewise.
(CFLAGS-s_modff-ppc64.c): Likewise.