powerpc64le: Add -mfloat128 to tst-strtod-nan-locale testcase
On powerpc64le, not all files can have the flag -mfloat128 passed as an
option on the compile command, since that could conflict with other
flags, such as -mno-vsx. Each file that needs the flag, gets it through
a CFLAGS-filename variable on sysdeps/powerpc/powerpc64le/Makefile.
The test cases tst-strtod-nan-locale and tst-wcstod-nan-locale are
missing this flag.
Tested for powerpc64le.
* sysdeps/powerpc/powerpc64le/Makefile
(CFLAGS-tst-strtod-nan-locale.c): New variable.
(CFLAGS-tst-wcstod-nan-locale.c): New variable.