https://developercommunity.visualstudio.com/t/warning-C5287:-operands-are-different-e/10877942?

It is not able to silence "operands are different enum types"
warnings, even using an explicit cast, as the message says.

Windows 11 SDK Version 10.0.26100.0 introduced a new internal inline
function in ucrt/corecrt_math.h.  Even it appears in object files and
will be included in the DEF file, it will be removed from the DLL and
result in a linker error.

	Define `incflags` also on mswin

When out-of-place build, and revision.h does not exist in the source
directory, `VPATH` fallbacks to the current directory.

There's no mjit_compile.inc, so no need to use this prefix anymore.

* Windows: Fix warning about undefined if_indextoname()

* Windows: Fix UNIXSocket on MINGW and make .pair more reliable

* Windows: Use nonblock=true for read tests with scheduler

* Windows: Move socket detection from File.socket? to File.stat

Add S_IFSOCK to Windows and interpret reparse points accordingly.
Enable tests that work now.

* Windows: Use wide-char functions to UNIXSocket

This fixes behaviour with non-ASCII characters.
It also fixes deletion of temporary UNIXSocket.pair files.

* Windows: Add UNIXSocket tests for specifics of Windows impl.

* Windows: fix VC build due to missing _snwprintf

Avoid usage of _snwprintf, since it fails linking ruby.dll like so:

  linking shared-library x64-vcruntime140-ruby320.dll
  x64-vcruntime140-ruby320.def : error LNK2001: unresolved external symbol snwprintf
  x64-vcruntime140-ruby320.def : error LNK2001: unresolved external symbol vsnwprintf_l

whereas linking miniruby.exe succeeds.

This patch uses snprintf on the UTF-8 string instead.

Also remove branch GetWindowsDirectoryW, since it doesn't work.

* Windows: Fix dangling symlink test failures

Co-authored-by: Lars Kanis <kanis@comcard.de>