[Bug libstdc++/89464] shared_ptr_base.h: error: '__tag' was not declared in this scope (gcc-8.3.0 regression?)

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89464

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #4)
> The problem is in https://github.com/Silicondust/libhdhomerun:
> hdhomerun_os_posix.h
> Which does:
> #if !defined(alignas)
> #define alignas(n) __attribute__((aligned(n)))
> #endif

This would be less broken as:

#if !defined(__cplusplus) && !defined(alignas)
#define alignas(n) __attribute__((aligned(n)))
#endif