aligned_alloc: remove old __MSVCRT_VERSION__ checks for mingw-w64

In upstream mingw-w64 the default value of __MSVCRT_VERSION__ was recently
changed from 0x700 to 0x600, causing boost/align to fall back to a
mingw-w64 provided _aligned_malloc for pre-winxp targets instead of using
the default one. See this for details:
mingw-w64/mingw-w64@90d3f33

_aligned_malloc is available in msvcrt.dll since WinXP, according to
https://github.com/mingw-w64/mingw-w64/blob/03d8a40f57649fbb773f1cdbe3a760f5e0943e76/mingw-w64-crt/lib-common/msvcrt.def.in#L1175-L1206,
so assuming boost/align does not support things older than WinXP, just remove
the checks and use one implementation for all of Windows instead.

_aligned_malloc is provided by mingw-w64 itself since 2009, so this change should
not affect compatibility with any of the currently used mingw-w64 versions.

Author: lazka

include/boost/align/aligned_alloc.hpp

@@ -22,12 +22,8 @@ Distributed under the Boost Software License, Version 1.0.
 #include <boost/align/detail/aligned_alloc.hpp>
 #elif defined(BOOST_ALIGN_USE_NEW)
 #include <boost/align/detail/aligned_alloc_new.hpp>
-#elif defined(_MSC_VER) && !defined(UNDER_CE)
+#elif defined(_WIN32) && !defined(UNDER_CE)
 #include <boost/align/detail/aligned_alloc_msvc.hpp>
-#elif defined(__MINGW32__) && (__MSVCRT_VERSION__ >= 0x0700)
-#include <boost/align/detail/aligned_alloc_msvc.hpp>
-#elif defined(__MINGW32__)
-#include <boost/align/detail/aligned_alloc_mingw.hpp>
 #elif MAC_OS_X_VERSION_MIN_REQUIRED >= 1090
 #include <boost/align/detail/aligned_alloc_posix.hpp>
 #elif MAC_OS_X_VERSION_MIN_REQUIRED >= 1060