gl: Define default value for GST_GL_HAVE_WINDOW_GBM
Thus, silent compiler's warning:
"GST_GL_HAVE_WINDOW_GBM" is not defined, evaluates to 0 [-Wundef]
diff --git a/gst-libs/gst/gl/meson.build b/gst-libs/gst/gl/meson.build
index f5f39b8..d9f8dfa 100644
--- a/gst-libs/gst/gl/meson.build
+++ b/gst-libs/gst/gl/meson.build
@@ -105,6 +105,7 @@
'GST_GL_HAVE_WINDOW_DISPMANX',
'GST_GL_HAVE_WINDOW_EAGL',
'GST_GL_HAVE_WINDOW_VIV_FB',
+ 'GST_GL_HAVE_WINDOW_GBM',
'GST_GL_HAVE_PLATFORM_EGL',
'GST_GL_HAVE_PLATFORM_GLX',