Annotate or fix FIXMEs in LLVM bindings and metadata code

Fixed up a few FIXMEs in lib/llvm to use more descriptive data
types. Covered FIXMEs in metadata::{creader, csearch, decoder} and
one in encoder.

src/rustc/metadata/encoder.rs

@@ -20,7 +20,6 @@ import std::ebml::serializer;
 import syntax::ast;
 import syntax::diagnostic::span_handler;
 
-export link_meta;
 export encode_parms;
 export encode_metadata;
 export encoded_ty;
@@ -33,9 +32,6 @@ export encode_ctxt;
 export write_type;
 export encode_def_id;
 
-// FIXME: This probably belongs somewhere else
-type link_meta = {name: str, vers: str, extras_hash: str};
-
 type abbrev_map = map::hashmap<ty::t, tyencode::ty_abbrev>;
 
 type encode_inlined_item = fn@(ecx: @encode_ctxt,
@@ -916,7 +912,7 @@ fn encode_meta_item(ebml_w: ebml::writer, mi: meta_item) {
             ebml_w.end_tag();
             ebml_w.end_tag();
           }
-          _ {/* FIXME (#611) */ }
+          _ {/* FIXME (#623): encode other variants */ }
         }
       }
       meta_list(name, items) {