[Bug libstdc++/69881] with gcc-6 of today building gcc-4.9 fails

[bernd.edlinger at hotmail dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69881

--- Comment #8 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
BTW:

the free-standing cstddef is also buggy:

#define __need_size_t
#define __need_ptrdiff_t
#define __need_NULL
#define __need_offsetof
#include_next <stddef.h>

but GCC's stddef.h does not implement __need_offsetof.
in the contrary, offsetof is not defined when any of the implemented
__need_XXX macros is set.

$prefix/lib/gcc/x86_64-pc-linux-gnu/6.0.0/include/stddef.h:

#ifdef _STDDEF_H

/* Offset of member MEMBER in a struct of type TYPE. */
#define offsetof(TYPE, MEMBER) __builtin_offsetof (TYPE, MEMBER)