common/build-helper: pass a full path for native builds in cmake-wxWidgets-gtk3.

At least KiCAD tries to find wx-config-gtk3 in the current directory,
without looking for it in PATH, so the build fails. Actually give it a
full path, like we do for the cross build case.

common/build-helper/cmake-wxWidgets-gtk3.sh

@@ -1,5 +1,5 @@
 if [ "$CROSS_BUILD" ]; then
 	export WX_CONFIG=${XBPS_WRAPPERDIR}/wx-config-gtk3
 else
-	export WX_CONFIG=wx-config-gtk3
+	export WX_CONFIG=/usr/bin/wx-config-gtk3
 fi