configure: add check for w32threads to enable it automatically

configure

@@ -2447,7 +2447,6 @@ case $target_os in
             disable network
         else
             target_os=mingw32
-            enable_weak w32threads
         fi
         LIBTARGET=i386
         if enabled x86_64; then
@@ -2852,6 +2851,10 @@ check_struct dxva2api.h DXVA_PictureParameters wDecodedPictureIndex
 disabled  zlib || check_lib   zlib.h      zlibVersion -lz   || disable  zlib
 disabled bzlib || check_lib2 bzlib.h BZ2_bzlibVersion -lbz2 || disable bzlib
 
+if ! disabled w32threads && ! enabled pthreads; then
+    check_func _beginthreadex && enable w32threads
+fi
+
 # check for some common methods of building with pthread support
 # do this before the optional library checks as some of them require pthreads
 if ! disabled pthreads && ! enabled w32threads; then