package/gdk-pixbuf: fix target loaders.cache

As reported by Rutger Sassen in
https://lists.buildroot.org/pipermail/buildroot/2022-March/638895.html,
target loaders.cache is broken since commit
75361a9aba042799040591fb84192802b137fc3a so fix it by prepending /usr/
to relative host paths

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/gdk-pixbuf/gdk-pixbuf.mk

@@ -70,14 +70,14 @@ endif
 # gdk-pixbuf requires the loaders.cache file populated to work properly
 # Rather than doing so at runtime, since the fs can be read-only, do so
 # here after building and installing to target.
-# And since the cache file will contain absolute host directory names we
-# need to sanitize (strip) them.
+# And since the cache file will contain relative host directory names we
+# need to prepend them with /usr/.
 ifeq ($(BR2_STATIC_LIBS),)
 define GDK_PIXBUF_UPDATE_CACHE
 	GDK_PIXBUF_MODULEDIR=$(HOST_DIR)/lib/gdk-pixbuf-2.0/2.10.0/loaders \
 		$(HOST_DIR)/bin/gdk-pixbuf-query-loaders \
 		> $(TARGET_DIR)/usr/lib/gdk-pixbuf-2.0/2.10.0/loaders.cache
-	$(SED) "s,$(HOST_DIR)/lib,/usr/lib,g" \
+	$(SED) 's,^"lib,"/usr/lib,g' \
 		$(TARGET_DIR)/usr/lib/gdk-pixbuf-2.0/2.10.0/loaders.cache
 endef
 GDK_PIXBUF_POST_INSTALL_TARGET_HOOKS += GDK_PIXBUF_UPDATE_CACHE