powerpc64le: Check for compiler features for float128

On powerpc64le, support for float128 will be enabled, which requires some
compiler features to be present.  This patch adds a configure test to check
for such features, which are provided for powerpc64le since GCC 6.2.

Tested for powerpc64 and powerpc64le.

	* INSTALL: Regenerate.
	* manual/install.texi (Recommended Tools for Compilation): Mention
	the powerpc64le-specific requirement in the manual.
	* sysdeps/powerpc/powerpc64le/configure.ac: New file with checks
	for the compiler features required for building float128.
	* sysdeps/powerpc/powerpc64le/configure: New, auto-generated file.

ChangeLog

@@ -1,3 +1,13 @@
+2017-06-26  Gabriel F. T. Gomes  <gftg@linux.vnet.ibm.com>
+	    Tulio Magno Quites Machado Filho  <tuliom@linux.vnet.ibm.com>
+
+	* INSTALL: Regenerate.
+	* manual/install.texi (Recommended Tools for Compilation): Mention
+	the powerpc64le-specific requirement in the manual.
+	* sysdeps/powerpc/powerpc64le/configure.ac: New file with checks
+	for the compiler features required for building float128.
+	* sysdeps/powerpc/powerpc64le/configure: New, auto-generated file.
+
 2017-06-26  Tulio Magno Quites Machado Filho  <tuliom@linux.vnet.ibm.com>
 
 	* malloc/tst-alloc_buffer.c (test_misaligned): Cast to char

INSTALL

@@ -428,6 +428,11 @@ build the GNU C Library:
      better code.  As of release time, GCC 6.3 is the newest compiler
      verified to work to build the GNU C Library.
 
+     For PowerPC 64-bits little-endian (powerpc64le), GCC 6.2 or higher
+     is required.  This compiler version is the first to provide the
+     features required for building the GNU C Library with support for
+     '_Float128'.
+
      For multi-arch support it is recommended to use a GCC which has
      been built with support for GNU indirect functions.  This ensures
      that correct debugging information is generated for functions

manual/install.texi

@@ -475,6 +475,10 @@ the newest version of the compiler that is known to work for building
 release time, GCC 6.3 is the newest compiler verified to work to build
 @theglibc{}.
 
+For PowerPC 64-bits little-endian (powerpc64le), GCC 6.2 or higher is
+required.  This compiler version is the first to provide the features
+required for building @theglibc{} with support for @code{_Float128}.
+
 For multi-arch support it is recommended to use a GCC which has been built with
 support for GNU indirect functions.  This ensures that correct debugging
 information is generated for functions selected by IFUNC resolvers.  This

sysdeps/powerpc/powerpc64le/configure

@@ -0,0 +1,45 @@
+# This file is generated from configure.ac by Autoconf.  DO NOT EDIT!
+ # Local configure fragment for sysdeps/powerpc/powerpc64le.
+
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking if $CC supports binary128 floating point type" >&5
+$as_echo_n "checking if $CC supports binary128 floating point type... " >&6; }
+if ${libc_cv_compiler_powerpc64le_binary128_ok+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  save_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS -Werror -mfloat128"
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+__float128 a, b, c, d, e;
+int i;
+
+__float128
+foobar (__float128 x)
+{
+  a = __builtin_nansq ("0");
+  b = __builtin_huge_valq ();
+  c = __builtin_infq ();
+  d = __builtin_fabsq (x);
+  e = __builtin_nanq ("0");
+  i = __builtin_signbit (x);
+  return __builtin_copysignq (x, x);
+}
+
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  libc_cv_compiler_powerpc64le_binary128_ok=yes
+else
+  libc_cv_compiler_powerpc64le_binary128_ok=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+CFLAGS="$save_CFLAGS"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_compiler_powerpc64le_binary128_ok" >&5
+$as_echo "$libc_cv_compiler_powerpc64le_binary128_ok" >&6; }
+if test "$libc_cv_compiler_powerpc64le_binary128_ok" != "yes"; then :
+  critic_missing="$critic_missing binary128 floating point type (GCC >= 6.2) is required on powerpc64le."
+fi
+
+test -n "$critic_missing" && as_fn_error $? "*** $critic_missing" "$LINENO" 5

sysdeps/powerpc/powerpc64le/configure.ac

@@ -0,0 +1,32 @@
+GLIBC_PROVIDES dnl See aclocal.m4 in the top level source directory.
+# Local configure fragment for sysdeps/powerpc/powerpc64le.
+
+dnl Require binary128 floating point support on powerpc64le (available in
+dnl GCC 6.2).
+AC_CACHE_CHECK([if $CC supports binary128 floating point type],
+	       libc_cv_compiler_powerpc64le_binary128_ok, [dnl
+save_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS -Werror -mfloat128"
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+__float128 a, b, c, d, e;
+int i;
+
+__float128
+foobar (__float128 x)
+{
+  a = __builtin_nansq ("0");
+  b = __builtin_huge_valq ();
+  c = __builtin_infq ();
+  d = __builtin_fabsq (x);
+  e = __builtin_nanq ("0");
+  i = __builtin_signbit (x);
+  return __builtin_copysignq (x, x);
+}
+]])],
+		  [libc_cv_compiler_powerpc64le_binary128_ok=yes],
+		  [libc_cv_compiler_powerpc64le_binary128_ok=no])
+CFLAGS="$save_CFLAGS"])
+AS_IF([test "$libc_cv_compiler_powerpc64le_binary128_ok" != "yes"],
+      [critic_missing="$critic_missing binary128 floating point type (GCC >= 6.2) is required on powerpc64le."])
+
+test -n "$critic_missing" && AC_MSG_ERROR([*** $critic_missing])