package/webkitgtk: make gbm support optional

This was added upstream in commit:

https://github.com/WebKit/WebKit/commit/22e4c0386605d84f42f2d46fd20bdc46e3078498

The 'USE_OPENGL_OR_ES' flag is default ON, which will enable 'USE_GBM',
so ensure that we unset 'USE_GBM' if we don't have libgbm.

Signed-off-by: Thomas Devoogdt <thomas.devoogdt@barco.com>
Tested-by: Adrian Perez de Castro <aperez@igalia.com>
Acked-by: Adrian Perez de Castro <aperez@igalia.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit c06c0197f95c3ae3408469f7e0702a00d788feb6)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/webkitgtk/webkitgtk.mk

@@ -86,6 +86,13 @@ else
 WEBKITGTK_CONF_OPTS += -DENABLE_GLES2=OFF
 endif
 
+ifeq ($(BR2_PACKAGE_HAS_LIBGBM),y)
+WEBKITGTK_CONF_OPTS += -DUSE_GBM=ON
+WEBKITGTK_DEPENDENCIES += libgbm
+else
+WEBKITGTK_CONF_OPTS += -DUSE_GBM=OFF
+endif
+
 ifeq ($(BR2_PACKAGE_LIBGTK3_X11),y)
 WEBKITGTK_CONF_OPTS += -DENABLE_X11_TARGET=ON
 WEBKITGTK_DEPENDENCIES += libgl \