[lib] Include full file path as cache key in ParseModel

Before, the hashtbl used to only contain as a key the name
of the file to be looked up. This causes issues when multiple
libdirs with conflicting file names are used across the same
run of herd. This eliminates this issues by adapting the keys
of this hashtbl so that they contain the full path of the
file, thus avoiding conflicts.

Author: TiberiuBucur

lib/parseModel.ml

@@ -73,12 +73,11 @@ module Make(O:Config) = struct
     (opts,txt,set_text pp code)
 
   let find_parse fname =
-    try Hashtbl.find t fname
+    let fname = O.libfind fname in
+    try fname, Hashtbl.find t fname
     with Not_found ->
-      let key = fname in
-      let fname = O.libfind fname in
       let r = Misc.input_protect (do_parse fname) fname in
-      Hashtbl.add t key (fname,r) ;
+      Hashtbl.add t fname r ;
       fname,r
 
   let parse fname = let _,r = find_parse fname in r