Both mpv and ffmpeg have their own internal pthreads wrappers. The mpv
one has been recently enabled by default as well. (It didn't work on XP,
but we dropped XP support.)
libwaio was added due to the complete inability to cancel synchronous
I/O cleanly using the public Windows API in Windows XP. Even calling
TerminateThread on the thread performing I/O was a bad solution, because
the TerminateThread function in XP would leak the thread's stack.
In Vista and up, however, this is no longer a problem. CancelIoEx can
cancel synchronous I/O running on other threads, allowing the thread to
exit cleanly, so replace libwaio usage with native Vista API functions.
It should be noted that this change also removes the hack added in
8a27025 for preventing a deadlock that only seemed to happen in Windows
XP. KB2009703 says that Vista and up are not affected by this, due to a
change in the implementation of GetFileType, so the hack should not be
needed anymore.
mpv can be built natively on a Windows machine using MSYS2. Add detailed
instructions on how to build and merge them with the existing
instructions for cross-compilation.
