Re-enable windows backends in autotool
AC_LANG_SOURCE only takes one argument, ignored the others.
Closes #542 (closed)
The effects of this are visible in mingw64 (MSYS2). Running autogen.sh you can see win32 backends were previously disabled (see issue for a few more details)
Should mention, the failing program looks the same as with AC_LANG_SOURCE with one argument, choke me
was not moved to the main(). Doesn't really matter which way, it just didn't appear as I would have expected.