asn1: Better handling of >63 named bits/ints

First, we enlarge Member's val field to int64_t.

Then we warn about skipping 2int, int2, and parse units glue for such
things with too-large members.

And we error out when generating the template for such things with
>UINT32_MAX members.

What about too-negative members?  That could be a thing for INTEGER /
ENUMERATED.  We'll look at that later.

lib/asn1/symbol.h

@@ -91,7 +91,7 @@ struct member {
     char *name;
     char *gen_name;
     char *label;
-    int val;
+    int64_t val;
     int optional;
     int ellipsis;
     struct type *type;