Support __STDC_WANT_IEC_60559_FUNCS_EXT__ feature test macro.

This patch implements support for the
__STDC_WANT_IEC_60559_FUNCS_EXT__ feature test macro, following the
__GLIBC_USE approach used for other ISO C feature test macros.
Currently this only affects the exp10 functions (which glibc has had
for a long time).

Tested for x86_64 and x86 (testsuite, and that installed stripped
shared libraries are unchanged by the patch).

	* bits/libc-header-start.h (__GLIBC_USE_IEC_60559_FUNCS_EXT): New
	macro.
	* include/features.h (__STDC_WANT_IEC_60559_FUNCS_EXT__):
	Document.
	* manual/creature.texi (__STDC_WANT_IEC_60559_FUNCS_EXT__):
	Document macro.
	* manual/math.texi (exp10): Document as ISO from TS 18661-4:2015.
	(exp10f): Likewise.
	(exp10l): Likewise.
	* math/bits/mathcalls.h (exp10): Declare if
	[__GLIBC_USE (IEC_60559_FUNCS_EXT)], not [__USE_GNU].

1 files changed, 2 insertions, 0 deletions

diff --git a/include/features.h b/include/features.h
index 554c5c888a..650d4c5e12 100644
--- a/include/features.h
+++ b/include/features.h
@@ -26,6 +26,8 @@
    _ISOC11_SOURCE	Extensions to ISO C99 from ISO C11.
    __STDC_WANT_LIB_EXT2__ Extensions to ISO C99 from TR 27431-2:2010.
    __STDC_WANT_IEC_60559_BFP_EXT__ Extensions to ISO C11 from TS 18661-1:2014.
+   __STDC_WANT_IEC_60559_FUNCS_EXT__ Extensions to ISO C11 from
+			TS 18661-4:2015.
    _POSIX_SOURCE	IEEE Std 1003.1.
    _POSIX_C_SOURCE	If ==1, like _POSIX_SOURCE; if >=2 add IEEE Std 1003.2;
 			if >=199309L, add IEEE Std 1003.1b-1993;