fftools/ffprobe: Disable stderr buffering on Windows

An identical call exists in ffmpeg.c

With POSIX/glibc, stderr is already unbuffered (or line-buffered when
a terminal is connected), but not in case of MSVCRT.
Explicitly calling setvbuf() like in this commit, makes the Windows
runtime behave like POSIX, giving the same “print immediately” behavior.

Signed-off-by: softworkz <softworkz@hotmail.com>

fftools/ffprobe.c

@@ -3081,6 +3081,8 @@ int main(int argc, char **argv)
 
     init_dynload();
 
+    setvbuf(stderr, NULL, _IONBF, 0); /* win32 runtime needs this */
+
     av_log_set_flags(AV_LOG_SKIP_REPEATED);
 
     options = real_options;