pppd: fix build with musl

Signed-off-by: Felix Fietkau <[email protected]>

SVN-Revision: 41404

package/network/services/ppp/Makefile

@@ -171,6 +171,9 @@ else
   MAKE_FLAGS += HAVE_MULTILINK=
 endif
 
+ifdef CONFIG_USE_MUSL
+  MAKE_FLAGS += USE_LIBUTIL=
+endif
 
 define Build/InstallDev
 	$(INSTALL_DIR) $(1)/usr/include