package/cloop: needs _GNU_SOURCE

host-cloop needs _GNU_SOURCE for loff_t otherwise build fails with gcc
8.3.0 on:
extract_compressed_fs.c: In function 'main':
extract_compressed_fs.c:55:2: error: unknown type name 'loff_t'; did you mean 'off_t'?
  loff_t *offsets;

Fixes:
 - No autobuilder failures

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit edf97df877694632111c029a0350732d8beca568)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/cloop/cloop.mk

@@ -13,7 +13,8 @@ CLOOP_LICENSE_FILES = README advancecomp-1.15/COPYING
 HOST_CLOOP_DEPENDENCIES = host-zlib
 
 define HOST_CLOOP_BUILD_CMDS
-	$(HOST_CONFIGURE_OPTS) $(MAKE1) -C $(@D) APPSONLY=yes
+	$(HOST_CONFIGURE_OPTS) $(MAKE1) -C $(@D) APPSONLY=yes \
+		CFLAGS="$(HOST_CFLAGS) -D_GNU_SOURCE"
 endef
 
 define HOST_CLOOP_INSTALL_CMDS