Define and use libm_alias_float128.

Continuing the process of setting up common macros for libm function
aliases, with a view to using them to define _FloatN / _FloatNx
aliases in future, this patch adds a libm_alias_float128 macro and
uses it in the type-generic templates.  (_Float128 functions will end
up with _Float64x aliases on powerpc64le, but not on x86_64/x86/ia64
because _Float64x has long double format there, and the macro will
provide a single place for the conditionals for that choice, as well
as for once ldbl-128 functions always build *f128 and need
conditionals for whether to have *l aliases.)

Tested for x86_64.  Also tested with build-many-glibcs.py that
installed stripped shared libraries are unchanged by the patch.

	* sysdeps/generic/libm-alias-float128.h: New file.
	* sysdeps/generic/math-type-macros-float128.h: Include
	<libm-alias-float128.h>.
	[!declare_mgen_alias] (declare_mgen_alias): Define macro.

2 files changed, 41 insertions, 0 deletions

diff --git a/sysdeps/generic/libm-alias-float128.h b/sysdeps/generic/libm-alias-float128.h
new file mode 100644
index 0000000000..6bb1cb1117
--- /dev/null
+++ b/sysdeps/generic/libm-alias-float128.h
@@ -0,0 +1,36 @@
+/* Define aliases for libm _Float128 functions.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _LIBM_ALIAS_FLOAT128_H
+#define _LIBM_ALIAS_FLOAT128_H
+
+/* Define aliases for a _Float128 libm function that has internal name
+   FROM ## f128 ## R and public names TO ## suffix ## R for each
+   suffix of a supported floating-point type with the same format as
+   _Float128.  This should only be used for functions where such
+   public names exist for _FloatN types, not for
+   implementation-namespace exported names (where there is one name
+   per format, not per type) or for obsolescent functions not provided
+   for _FloatN types.  */
+#define libm_alias_float128_r(from, to, r)		\
+  weak_alias (from ## f128 ## r, to ## f128 ## r)
+
+/* Likewise, but without the R suffix.  */
+#define libm_alias_float128(from, to) libm_alias_float128_r (from, to, )
+
+#endif
diff --git a/sysdeps/generic/math-type-macros-float128.h b/sysdeps/generic/math-type-macros-float128.h
index 5d734db29f..3e69c17f65 100644
--- a/sysdeps/generic/math-type-macros-float128.h
+++ b/sysdeps/generic/math-type-macros-float128.h
@@ -32,6 +32,11 @@
 
 #define M_MLIT(c) c ## f128
 
+#include <libm-alias-float128.h>
+
+#ifndef declare_mgen_alias
+# define declare_mgen_alias(from, to) libm_alias_float128 (from, to)
+#endif
 
 /* Supply the generic macros.  */
 #include <math-type-macros.h>