Define __STDC_WANT_IEC_60559_TYPES_EXT__ in tst-strtod-round-skeleton.c.
The tst-strtod-round-skeleton.c conditionals relating to handling of
_Float64x require associated <float.h> macros, which requires
__STDC_WANT_IEC_60559_TYPES_EXT__ to be defined before <float.h> is
included if _Float64x is supported. This patch adds the necessary
definition.
Tested for x86_64, including in conjunction with _Float64x support
patches.
* stdlib/tst-strtod-round-skeleton.c
(__STDC_WANT_IEC_60559_TYPES_EXT__): Define before including
headers.