[Mingw-w64-public] __C_specific_handler accessible for __IA_64__ but not for __X86_64

[k***@free.fr]

Hello,

I'm trying to compile Gcc-7.0.1 and mingw-w64-5.0.2 in 64bits, using
MSYS.

I would like to enable the libsanitizer support, but one of the windows
depentant files complains about unknown __C_specific_handler.

Having a look for this function, i found it in the expct.h header, but
surrounded like this :

#if (defined(_X86_) && !defined(__x86_64))
struct _EXCEPTION_RECORD;
struct _CONTEXT;

EXCEPTION_DISPOSITION __cdecl _except_handler(struct _EXCEPTION_RECORD
*_ExceptionRecord,
void
*_EstablisherFrame,struct _CONTEXT *_ContextRecord,
void
*_DispatcherContext);
#elif defined(__ia64__)

typedef struct _EXCEPTION_POINTERS *Exception_info_ptr;
struct _EXCEPTION_RECORD;
struct _CONTEXT;
struct _DISPATCHER_CONTEXT;

__MINGW_EXTENSION _CRTIMP EXCEPTION_DISPOSITION __cdecl
__C_specific_handler (struct _EXCEPTION_RECORD *_ExceptionRecord,

unsigned __int64 _MemoryStackFp,unsigned __int64 _BackingStoreFp,

struct _CONTEXT *_ContextRecord,struct _DISPATCHER_CONTEXT
*_DispatcherContext,

unsigned __int64 _GlobalPointer);
#elif defined(__x86_64)

struct _EXCEPTION_RECORD;
struct _CONTEXT;
#endif

(end of line are mine)

Is there any reason to make this extension aviable for IA_64 only or
could we considere to make it aviable for X86_64 too?