fix musl static build

Don't define NO_DIR if no directory library is needed

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

diff -Nura zip30.orig/unix/configure zip30/unix/configure
--- zip30.orig/unix/configure	2021-08-31 21:29:55.219967136 +0200
+++ zip30/unix/configure	2021-08-31 21:50:48.239280513 +0200
@@ -569,8 +569,8 @@
   done
   if [ ${OPT} ]; then
     LFLAGS2="${LFLAGS2} ${OPT}"
-  else
-    CFLAGS="${CFLAGS} -DNO_DIR"
+  #else
+  #  CFLAGS="${CFLAGS} -DNO_DIR"
   fi
 fi