Ensure C99 and C11 interfaces are available for C++ [BZ #21326]

This patch ensures that the C99 and C11 features required by C++ are
defined according to the value of the __cplusplus macro, and not just
because G++ always defines _GNU_SOURCE.  This will allow G++ to stop
defining _GNU_SOURCE some day, without causing the C99 and C11
interfaces to disappear for C++ programs.

	[BZ #21326]
	* include/features.h [__cplusplus >= 201103] (__USE_ISOC99): Define.
	[__cplusplus >= 201703] (__USE_ISOCXX17, __USE_ISOC11): Define.
	* math/Makefile (test-math-cxx11): New test.
	* math/test-math-cxx11.cc: New file.

1 files changed, 160 insertions, 0 deletions

diff --git a/math/test-math-cxx11.cc b/math/test-math-cxx11.cc
new file mode 100644
index 0000000..8417cdd
--- /dev/null
+++ b/math/test-math-cxx11.cc
@@ -0,0 +1,160 @@
+/* Test C99 math functions are available in C++11 without _GNU_SOURCE.
+   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/>.  */
+
+#undef _GNU_SOURCE
+#undef _DEFAULT_SOURCE
+#undef _XOPEN_SOURCE
+#undef _POSIX_SOURCE
+#undef _POSIX_C_SOURCE
+// __STRICT_ANSI__ gets defined by -std=c++11 in CFLAGS
+#include <math.h>
+#include <stdio.h>
+
+static int
+do_test (void)
+{
+#ifdef _GNU_SOURCE
+  printf ("FAIL: _GNU_SOURCE is defined.\n");
+  return 1;
+#endif
+
+#if __cplusplus >= 201103L
+  /* Verify that C11 math functions and types are defined for C++11,
+     without _GNU_SOURCE being defined. [BZ #21326] */
+  (void) FP_INFINITE;
+  (void) FP_NAN;
+  (void) FP_NORMAL;
+  (void) FP_SUBNORMAL;
+  (void) FP_ZERO;
+  double_t d = 1.0;
+  (void) d;
+  float_t f = 1.0f;
+  (void) f;
+  (void) acosh;
+  (void) acoshf;
+  (void) acoshl;
+  (void) asinh;
+  (void) asinhf;
+  (void) asinhl;
+  (void) atanh;
+  (void) atanhf;
+  (void) atanhl;
+  (void) cbrt;
+  (void) cbrtf;
+  (void) cbrtl;
+  (void) copysign;
+  (void) copysignf;
+  (void) copysignl;
+  (void) erf;
+  (void) erff;
+  (void) erfl;
+  (void) erfc;
+  (void) erfcf;
+  (void) erfcl;
+  (void) exp2;
+  (void) exp2f;
+  (void) exp2l;
+  (void) expm1;
+  (void) expm1f;
+  (void) expm1l;
+  (void) fdim;
+  (void) fdimf;
+  (void) fdiml;
+  (void) fma;
+  (void) fmaf;
+  (void) fmal;
+  (void) fmax;
+  (void) fmaxf;
+  (void) fmaxl;
+  (void) fmin;
+  (void) fminf;
+  (void) fminl;
+  (void) hypot;
+  (void) hypotf;
+  (void) hypotl;
+  (void) ilogb;
+  (void) ilogbf;
+  (void) ilogbl;
+  (void) lgamma;
+  (void) lgammaf;
+  (void) lgammal;
+  (void) llrint;
+  (void) llrintf;
+  (void) llrintl;
+  (void) llround;
+  (void) llroundf;
+  (void) llroundl;
+  (void) log1p;
+  (void) log1pf;
+  (void) log1pl;
+  (void) log2;
+  (void) log2f;
+  (void) log2l;
+  (void) logb;
+  (void) logbf;
+  (void) logbl;
+  (void) lrint;
+  (void) lrintf;
+  (void) lrintl;
+  (void) lround;
+  (void) lroundf;
+  (void) lroundl;
+  (void) nan;
+  (void) nanf;
+  (void) nanl;
+  (void) nearbyint;
+  (void) nearbyintf;
+  (void) nearbyintl;
+  (void) nextafter;
+  (void) nextafterf;
+  (void) nextafterl;
+  (void) nexttoward;
+  (void) nexttowardf;
+  (void) nexttowardl;
+  (void) remainder;
+  (void) remainderf;
+  (void) remainderl;
+  (void) remquo;
+  (void) remquof;
+  (void) remquol;
+  (void) rint;
+  (void) rintf;
+  (void) rintl;
+  (void) round;
+  (void) roundf;
+  (void) roundl;
+  (void) scalbln;
+  (void) scalblnf;
+  (void) scalblnl;
+  (void) scalbn;
+  (void) scalbnf;
+  (void) scalbnl;
+  (void) tgamma;
+  (void) tgammaf;
+  (void) tgammal;
+  (void) trunc;
+  (void) truncf;
+  (void) truncl;
+  printf ("PASS: C11 math functions present in C++11 without _GNU_SOURCE.\n");
+#else
+  printf ("UNSUPPORTED: C++11 not enabled.\n");
+#endif
+  return 0;
+}
+
+#include <support/test-driver.c>