Fix libcxx MSVC C++17 redefinition of 'align_val_t'

[fcharlie]

Summary

When use

clang-cl -std:c++17 -Iinclude\c++\v1 hello.cc c++.lib

An error occurred:

In file included from hello.cc:1:
In file included from include\c++\v1\iostream:38:
In file included from include\c++\v1\ios:216:
In file included from include\c++\v1\__locale:15:
In file included from include\c++\v1\string:477:
In file included from include\c++\v1\string_view:176:
In file included from include\c++\v1\__string:56:
In file included from include\c++\v1\algorithm:643:
In file included from include\c++\v1\memory:656:
include\c++\v1\new(165,29):  error: redefinition of 'align_val_t'
enum class _LIBCPP_ENUM_VIS align_val_t : size_t { };
                            ^
C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.12.25827\include\vcruntime_new.h(43,16):  note:
      previous definition is here
    enum class align_val_t : size_t {};
               ^
1 error generated.

vcruntime_new.h has defined align_val_t, libcxx need hide align_val_t.

[STL_MSFT]

Seems reasonable to me.

[fcharlie]

In D42354#984067, @STL_MSFT wrote:

Seems reasonable to me.

Thanks

[mclow.lists]

I'm pretty sure I don't want to know what MSFT is doing putting align_val_t in *that* header file.

Now I'm wondering if those values __zero and __max are actually used.

[fcharlie]

In D42354#988656, @mclow.lists wrote:

I'm pretty sure I don't want to know what MSFT is doing putting align_val_t in *that* header file.

Now I'm wondering if those values __zero and __max are actually used.

Use

grep "__zero" -Rn .

There's no place to use __zero and __max. only C++03

[fcharlie]

This comment was removed by fcharlie.

[compnerd]

I think that if we can remove the __zero and __max, we should do that, but that is better done as a separate change.

[fcharlie]

This comment was removed by fcharlie.

[fcharlie]

@compnerd Please commit this, Thanks

[EricWF]

Committed as r324853.

include/new

 
 #endif  // defined(_LIBCPP_BUILDING_NEW) || (_LIBCPP_STD_VER > 11)
 
+#if !defined(_LIBCPP_ABI_MICROSOFT) || defined(_LIBCPP_NO_VCRUNTIME)
 #if !defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION) || _LIBCPP_STD_VER > 14
 #ifndef _LIBCPP_CXX03_LANG
 enum class _LIBCPP_ENUM_VIS align_val_t : size_t { };

 enum align_val_t { __zero = 0, __max = (size_t)-1 };
 #endif
 #endif
+#endif
 
 }  // std