m4/gst-gl: Add dummy GST_GL_HAVE_WINDOW_WINRT

Add a dummy define to make fix the autotools build for now. To
actually build WinRT support, use the meson build.

m4/gst-gl.m4

@@ -744,6 +744,7 @@ GST_GL_HAVE_WINDOW_DISPMANX=0
 GST_GL_HAVE_WINDOW_EAGL=0
 GST_GL_HAVE_WINDOW_VIV_FB=0
 GST_GL_HAVE_WINDOW_GBM=0
+GST_GL_HAVE_WINDOW_WINRT=0
 
 if test "x$HAVE_WINDOW_X11" = "xyes"; then
   GL_WINDOWS="x11 $GL_WINDOWS"
@@ -792,6 +793,7 @@ GL_CONFIG_DEFINES="$GL_CONFIG_DEFINES
 #define GST_GL_HAVE_WINDOW_EAGL $GST_GL_HAVE_WINDOW_EAGL
 #define GST_GL_HAVE_WINDOW_VIV_FB $GST_GL_HAVE_WINDOW_VIV_FB
 #define GST_GL_HAVE_WINDOW_GBM $GST_GL_HAVE_WINDOW_GBM
+#define GST_GL_HAVE_WINDOW_WINRT $GST_GL_HAVE_WINDOW_WINRT
 "
 
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