libgd: add conflicts to each other

The full variant should conflict with the default variant. This prevents that
libgd and libgd-full could be installed side by side, and also, the full
variant should provide the libgd. Otherwise, if you install libgd-full,
you can not install vnstat.

Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
(cherry picked from commit 42b36b7180)

libs/libgd/Makefile

@@ -43,6 +43,8 @@ define Package/libgd-full
   DEPENDS+=+libtiff +libfreetype
   TITLE+=(full)
   VARIANT:=full
+  PROVIDES:=libgd
+  CONFLICTS:=libgd
 endef
 
 define Package/libgd/description/default