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.

1 files changed, 4 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 2a65383f12..be9ed44d83 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2017-11-24  Joseph Myers  <joseph@codesourcery.com>
 
+	* stdlib/tst-strtod-round-skeleton.c
+	(__STDC_WANT_IEC_60559_TYPES_EXT__): Define before including
+	headers.
+
 	* math/gen-tgmath-tests.py (Type.init_types): Pass suffix argument
 	for combinations of long double with _Float64 and _Float64x.