libctf: create, types: conflicting types

The conflicting type kind is a CTF-specific prefix kind consisting purely of
an optional translation unit name.  It takes the place of the old hidden
bit: we have already seen it used to prefix types added with a
CTF_ADD_NONROOT flag.  The deduplicator will also use them to label
conflicting types from different TUs smushed into the same dict by the
CU-mapping mechanism: unlike the hidden bit, with this scheme users can tell
which CUs the conflicting types came from.

New API:

+int ctf_type_conflicting (ctf_dict_t *, ctf_id_t, const char **cuname);
+int ctf_set_conflicting (ctf_dict_t *, ctf_id_t, const char *);

(Frankly I expect ctf_set_conflicting to be used only by deduplicators and
things like that, but if we provide an option to query something we should
also provide an option to produce it...)

include/ctf-api.h

@@ -674,6 +674,13 @@ extern int ctf_type_kind (ctf_dict_t *, ctf_id_t);
 
 extern int ctf_type_kind_forwarded (ctf_dict_t *, ctf_id_t);
 
+/* Return nonzero if this type is conflicting, zero if it's not, < 0 on error; if
+   CUNAME is set, set it to the name of the conflicting compilation unit for the
+   passed-in type (which may be a null string if the cuname is not known, or if
+   this is not a conflicting type).  */
+
+extern int ctf_type_conflicting (ctf_dict_t *, ctf_id_t, const char **cuname);
+
 /* Return the type a pointer, typedef, cvr-qual, or slice refers to, or return
    an ECTF_NOTREF error otherwise.  ctf_type_kind pretends that slices are
    actually the type they are a slice of: this is usually want you want, but if
@@ -1008,7 +1015,13 @@ extern ctf_id_t ctf_add_section_variable (ctf_dict_t *, uint32_t,
 
 extern int ctf_set_array (ctf_dict_t *, ctf_id_t, const ctf_arinfo_t *);
 
-/* Add a function oor object symbol type with a particular name, without saying
+/* Mark a type as conflicting, residing in some other translation unit with a
+   given name.  The type is hidden from all name lookups, just like
+   CTF_ADD_NONROOT.  */
+
+extern int ctf_set_conflicting (ctf_dict_t *, ctf_id_t, const char *);
+
+/* Add a function or object symbol type with a particular name, without saying
    anything about the actual symbol index.  (The linker will then associate them
    with actual symbol indexes using the ctf_link functions below.)  */