libstdc++: Don't fail if math_errhandling is not defined

Older glibc does not define math_errhandling with -ffast-math, in which
case floating-point exceptions are not used.

Signed-off-by: Matthias Kretz <m.kretz@gsi.de>
libstdc++-v3/ChangeLog:

	* include/experimental/bits/simd.h (__floating_point_flags): Do
	not rely on the presence of the math_errhandling macro.

diff --git a/libstdc++-v3/include/experimental/bits/simd.h b/libstdc++-v3/include/experimental/bits/simd.h
index d837d0e..c991e3f 100644 (file)
--- a/libstdc++-v3/include/experimental/bits/simd.h
+++ b/libstdc++-v3/include/experimental/bits/simd.h
@@ -283,11 +283,20 @@ constexpr inline bool __have_power_vmx = __have_power_vsx;
 
 namespace __detail
 {
+  constexpr bool __handle_fpexcept =
+#ifdef math_errhandling
+    math_errhandling & MATH_ERREXCEPT;
+#elif defined __FAST_MATH__
+    false;
+#else
+    true;
+#endif
+
   constexpr std::uint_least64_t
   __floating_point_flags()
   {
     std::uint_least64_t __flags = 0;
-    if constexpr (math_errhandling & MATH_ERREXCEPT)
+    if constexpr (__handle_fpexcept)
       __flags |= 1;
 #ifdef __FAST_MATH__
     __flags |= 1 << 1;