Declare some TS 18661-4 interfaces for C2X [committed]

[Joseph Myers <joseph@codesourcery.com>]

C2X (current version in git, postdating the most recent public draft
available as a PDF on the WG14 website) adds the interfaces from TS
18661-4, other than the reduction functions, as unconditionally
required and visible in <math.h> for hosted implementations; the
__STDC_WANT_IEC_60559_FUNCS_EXT__ macro is not included in C2X at all
(as the reduction functions aren't included at all, expected to end up
in a version of the TS updated to be relative to C2X).

This patch updates the glibc headers accordingly, following the same
pattern used for 18661-1 functions.  As the only 18661-4 functions
currently supported are the exp10 functions that have been in glibc
for a very long time, this means that in fact __GLIBC_USE
(IEC_60559_FUNCS_EXT) ends up being used only to determine the
definition of __GLIBC_USE_IEC_60559_FUNCS_EXT_C2X, not yet in any
headers other than bits/libc-header-start.h.

(I hope to add the other 18661-4 functions to glibc at some point; the
main complication is the current lack of MPFR support for many of
these functions.)

Tested for x86_64.  Committed.

2019-08-13  Joseph Myers  <joseph@codesourcery.com>

	* bits/libc-header-start.h (__GLIBC_USE_IEC_60559_FUNCS_EXT):
	Update comment.
	(__GLIBC_USE_IEC_60559_FUNCS_EXT_C2X): New macro.
	* bits/math-finite.h [__GLIBC_USE (IEC_60559_FUNCS_EXT)]: Change
	to [__GLIBC_USE (IEC_60559_FUNCS_EXT_C2X)].
	* math/bits/mathcalls.h [__GLIBC_USE (IEC_60559_FUNCS_EXT)]:
	Likewise.

diff --git a/bits/libc-header-start.h b/bits/libc-header-start.h
index f2acc5333e..2c7c6e00e0 100644
--- a/bits/libc-header-start.h
+++ b/bits/libc-header-start.h
@@ -60,13 +60,21 @@
 #endif
 
 /* ISO/IEC TS 18661-4:2015 defines the
-   __STDC_WANT_IEC_60559_FUNCS_EXT__ macro.  */
+   __STDC_WANT_IEC_60559_FUNCS_EXT__ macro.  Other than the reduction
+   functions, the symbols from this TS are enabled unconditionally in
+   C2X.  */
 #undef __GLIBC_USE_IEC_60559_FUNCS_EXT
 #if defined __USE_GNU || defined __STDC_WANT_IEC_60559_FUNCS_EXT__
 # define __GLIBC_USE_IEC_60559_FUNCS_EXT 1
 #else
 # define __GLIBC_USE_IEC_60559_FUNCS_EXT 0
 #endif
+#undef __GLIBC_USE_IEC_60559_FUNCS_EXT_C2X
+#if __GLIBC_USE (IEC_60559_FUNCS_EXT) || __GLIBC_USE (ISOC2X)
+# define __GLIBC_USE_IEC_60559_FUNCS_EXT_C2X 1
+#else
+# define __GLIBC_USE_IEC_60559_FUNCS_EXT_C2X 0
+#endif
 
 /* ISO/IEC TS 18661-3:2015 defines the
    __STDC_WANT_IEC_60559_TYPES_EXT__ macro.  */
diff --git a/bits/math-finite.h b/bits/math-finite.h
index 6141c12537..54cec8f8d8 100644
--- a/bits/math-finite.h
+++ b/bits/math-finite.h
@@ -67,7 +67,7 @@ __MATH_REDIRCALL (cosh, , (_Mdouble_));
 /* exp.  */
 __MATH_REDIRCALL (exp, , (_Mdouble_));
 
-#if __GLIBC_USE (IEC_60559_FUNCS_EXT)
+#if __GLIBC_USE (IEC_60559_FUNCS_EXT_C2X)
 /* exp10.  */
 __MATH_REDIRCALL (exp10, , (_Mdouble_));
 #endif
diff --git a/math/bits/mathcalls.h b/math/bits/mathcalls.h
index 3d1dc07d98..47808a2915 100644
--- a/math/bits/mathcalls.h
+++ b/math/bits/mathcalls.h
@@ -109,7 +109,7 @@ __MATHCALL (log10,, (_Mdouble_ __x));
 /* Break VALUE into integral and fractional parts.  */
 __MATHCALL (modf,, (_Mdouble_ __x, _Mdouble_ *__iptr)) __nonnull ((2));
 
-#if __GLIBC_USE (IEC_60559_FUNCS_EXT)
+#if __GLIBC_USE (IEC_60559_FUNCS_EXT_C2X)
 /* Compute exponent to base ten.  */
 __MATHCALL (exp10,, (_Mdouble_ __x));
 #endif

-- 
Joseph S. Myers
joseph@codesourcery.com