Windows master builds failing

[gamer191]

The Windows builds of the master branch are failing

I'm going to try to run tests to see which patch is causing the error (but I can't help much beyond that)

Test 1: does ffmpeg build successfully if the last 3 patches are deleted? Result: no (potentially caused by interference from the scheduled build, but I highly doubt it, based on the log)

Test 2: Does it build if we delete patches 2-6 (so only patch 1 applies)? Result: workflow failed, due to permissions error, but the part that was failing succeeded, so I'm calling it a success

Test 3: Does it build with patches 3-6 deleted? Result: workflow failed, due to error pruning old releases, but the part that was failing succeeded, so I'm calling it a success

As such, patch 3 is the problematic patch

CC @nihil-admirari

[nihil-admirari]

In file included from libavcodec/mfenc.c:32:
./compat/w32dlfcn.h: In function 'win32_dlopen':
./compat/w32dlfcn.h:62:9: error: implicit declaration of function 'utf8towchar' [-Werror=implicit-function-declaration]
   62 |     if (utf8towchar(name, &name_w))
      |         ^~~~~~~~~~~

Made wchar_filename.h include unconditional:

-#if (_WIN32_WINNT < 0x0602) || HAVE_WINRT
 #include "libavutil/wchar_filename.h"
-#endif

[gamer191]

Thanks