asn1: Make templating less fragile: test it more

`lib/asn1/check-gen.c` almost works with templates, and is a pretty
extensive test.  The only thing that fails is everything to do with
IMPLICIT tags (so, `test_implicit()`).

So now we compile `lib/asn1/test.asn1` both, w/ and w/o templating, and
we build two programs from `lib/asn1/check-gen.c`: `check-gen` and
`check-gen-template`, respectively linking with the non-templated and
the templated compilation of `lib/asn1/test.asn1`.

Because the template compiler still doesn't support IMPLICIT tagging
well, we disable testing of IMPLICIT tags in `check-gen-template`.

This will make it much harder to break the template compiler in the
future.

lib/asn1/check-gen.c

@@ -1016,6 +1016,7 @@ test_choice (void)
     return ret;
 }
 
+#ifdef IMPLICIT_TAGGING_WORKS
 static int
 cmp_TESTImplicit (void *a, void *b)
 {
@@ -1104,6 +1105,7 @@ test_implicit (void)
 
     return ret;
 }
+#endif
 
 static int
 cmp_TESTAlloc (void *a, void *b)
@@ -1881,7 +1883,9 @@ main(int argc, char **argv)
     DO_ONE(test_large_tag);
     DO_ONE(test_choice);
 
+#ifdef IMPLICIT_TAGGING_WORKS
     DO_ONE(test_implicit);
+#endif
 
     DO_ONE(test_taglessalloc);
     DO_ONE(test_optional);