Respect LDFLAGS

--- a/configure.ac
+++ b/configure.ac
@@ -288,15 +288,13 @@
 )
 AC_SUBST(LDLIBS)
 
-LDFLAGS=
 LIBDIRS=
 AC_ARG_WITH(libdirs,
 [  --with-libdirs          Specifies library directories (-Ldir1 -Ldir2).],
 LIBDIRS=$withval
-LDFLAGS=$withval
 AC_MSG_RESULT([Using extra library directories: $withval])
 )
-AC_SUBST(LDFLAGS)
+AC_SUBST(LIBDIRS)
 
 AC_CHECK_PROGS(PERL,perl,perl) AC_SUBST(PERL)