[libc++] Correct alignment condition

[smeenai]

Summary

The max alignment is a PE/COFF restriction, not an MSVC-specific
restriction; it also applies to gcc and clang when compiling for
Windows. Change the conditional to _WIN32 to reflect this.

[mclow.lists]

How is this different from D14259 ??

[smeenai]

It's not – I just wasn't aware of the existence of the other one :) That one's been stagnant for a long time though. One of these changes should be abandoned in favor of the other, and I'm fine doing it either way.

[smeenai]

@mclow.lists Do you have any preference between this and D14259? I'm fine either way, but I'd want one of them to be committed sooner rather than later.

[mclow.lists]

I will land this, and close the other one, too.

[mclow.lists]

Committed as revision 283621

include/type_traits

 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x40);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x80);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x100);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x200);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x400);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x800);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x1000);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x2000);
-// MSDN says that MSVC does not support alignment beyond 8192 (=0x2000)
-#if !defined(_LIBCPP_MSVC)
+// PE/COFF does not support alignment beyond 8192 (=0x2000)
+#if !defined(_WIN32)
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x4000);
-#endif // !_LIBCPP_MSVC
+#endif // !_WIN32
 
 #undef _CREATE_ALIGNED_STORAGE_SPECIALIZATION
 
 #ifndef _LIBCPP_HAS_NO_VARIADICS
 
 // aligned_union
 
 template <size_t _I0, size_t ..._In>