[PATCH 4/8] Add support for testing __STDC_WANT_IEC_60559_TYPES_EXT__

["Gabriel F. T. Gomes" <gftg@linux.vnet.ibm.com>]

From: "Paul E. Murphy" <murphyp@linux.vnet.ibm.com>

This is defined by TS 18661-3 for supporting the _FloatN
and _FloatNx types.

This will also implicitly enforce a minimum GCC 4.9.  Given
the standard is a C11 derivative, it would seem reasonable
to assume a C11 compiler with _Generic support.  This allows
for much simpler type classification macros which in theory
should be supported on any C11 compiler.

	* bits/libc-header-start.h:
	(__GLIBC_USR_IEC_60559_TYPES_EXT): New macro.
---
 bits/libc-header-start.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/bits/libc-header-start.h b/bits/libc-header-start.h
index ee6a876..251ff05 100644
--- a/bits/libc-header-start.h
+++ b/bits/libc-header-start.h
@@ -59,3 +59,18 @@
 #else
 # define __GLIBC_USE_IEC_60559_FUNCS_EXT 0
 #endif
+
+/* ISO/IEC TS 18661-3:2014 defines the
+   __STDC_WANT_IEC_60559_TYPES_EXT__ macro.
+
+   Note, as a tradeoff for keeping the headers simple, this will
+   require C11 Generic support.  Thus, GCC 4.9 is mandated when
+   requesting this support and using GCC.  */
+#undef __GLIBC_USE_IEC_60559_TYPES_EXT
+#if (defined __STDC_WANT_IEC_60559_TYPES_EXT__ || defined __USE_GNU)	   \
+   && defined __USE_ISOC11						   \
+   && ((defined __GNUC__ && __GNUC_PREREQ (4, 9)) || !defined __GNUC__)
+# define __GLIBC_USE_IEC_60559_TYPES_EXT 1
+#else
+# define __GLIBC_USE_IEC_60559_TYPES_EXT 0
+#endif
-- 
2.4.11