-AC_ARG_WITH(gmp, [ --with-gmp use external fast low-level functions from GNU MP 3.
- [default=yes]], ,with_gmp="yes")
+AC_ARG_WITH(gmp, AS_HELP_STRING([--with-gmp],
+ [use external fast low-level functions from GNU MP (default: yes).]),
+ with_gmp="$withval",
+ with_gmp="yes")