[libcxx] [libcxxabi] fix building with libc++ win32 threads for mingw-w64

[martell]

Summary

When bootstrapping with _LIBCPP_HAS_THREAD_API_WIN32 we need to set windows version to atleast 0x0600 for the fibersapi
We do not use these newer apis with the pthread version, this should be safe to do here regardless.

This is useful for environments that want c++11 threading but without using winpthreads.

[EricWF]

libcxxabi/trunk/cmake/config-ix.cmake

42

Same comment about -D_WIN32_WINNT=0x0600 as in D33388.

[martell]

@EricWF might make the most sense to have the review for -D_WIN32_WINNT=0x0600 here.

[martell]

committed the iconv removal in rL304026

[martell]

updated to just contain win32 thread api fix

[martell]

@EricWF I believe your concern was that 0x600 was Vista.
I only updated this to the min required version to build.
https://github.com/mirror/mingw-w64/blob/master/mingw-w64-headers/include/fibersapi.h#L17

[EricWF]

Why do we *need* to set it? Doesn't _WIN32_WINNT default to the current platform?

libcxx/trunk/cmake/config-ix.cmake

53

Shouldn't we use add_definitions ?

[martell]

In D33384#766084, @EricWF wrote:

Why do we *need* to set it? Doesn't _WIN32_WINNT default to the current platform?

Not for mingw-w64, that wouldn't make much sense in general because of cross compiling.
It defaults to` 0x502` here which is a bump above Windows XP, which support was dropped for when MS officially dropped support for that platform.
https://github.com/mingw-w64/mingw-w64/blob/master/mingw-w64-headers/crt/_mingw.h.in#L225

libcxx/trunk/cmake/config-ix.cmake

53

That makes sense.
I can change it to add_definitions

[martell]

updated to add_definitions

[EricWF]

This isn't a solution to the problem. It may work when compiling the library, but that's not the important part.
The bits of libc++ that use the fibers interface are in the headers, that means that _WINNT_VER must
also have the same value any time a libc++ header is included by a user. However this can only be
achieved by making the compiler pre-define _WINNT_VER, or by removing the nonsensically old
definition MinGW provides. Neither of these can be done by libc++.

For example:

#include <windows.h> // _WINNT_VER isn't yet defined. Fibers are not included
#include <thread> // libc++ is too late to change the definition.
// ERROR <thread> cannot be compiled.

[EricWF]

Yeah, after discussing this further this is MinGW's problem to fix.

MinGW is *WRONG* for defaulting the macro to such a low value. It should be defaulting it to the value of the target, not 0x502.
https://github.com/mingw-w64/mingw-w64/blob/master/mingw-w64-headers/crt/_mingw.h.in#L225

[martell]

The default is now configurable in mingw-w64

libcxx/trunk/cmake/config-ix.cmake

                         shell32 user32 kernel32 mingw32 ${MINGW_RUNTIME}
                         moldname mingwex msvcrt)
     list(APPEND CMAKE_REQUIRED_LIBRARIES ${MINGW_LIBRARIES})
+    add_definitions(-D_WIN32_WINNT=0x0600)
   endif()
   if (CMAKE_C_FLAGS MATCHES -fsanitize OR CMAKE_CXX_FLAGS MATCHES -fsanitize)
     set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize=all")

libcxxabi/trunk/cmake/config-ix.cmake

                         shell32 user32 kernel32 mingw32 ${MINGW_RUNTIME}
                         moldname mingwex msvcrt)
     list(APPEND CMAKE_REQUIRED_LIBRARIES ${MINGW_LIBRARIES})
+    add_definitions(-D_WIN32_WINNT=0x0600)
   endif()
   if (CMAKE_C_FLAGS MATCHES -fsanitize OR CMAKE_CXX_FLAGS MATCHES -fsanitize)
     set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize=all")