Handle the new warnings of OCaml 4.13

Warning 69 "mutable record field is never mutated":
  3 occurrences in backend/IRC.ml
  removed the "mutable" qualifier on these fields

Warning 70 "cannot find interface file"
  many .ml files have no .mli
  no strong motivation to add the .mli files
  turned off the warning in Makefile.extr

Author: xavierleroy

Makefile.extr

@@ -51,7 +51,7 @@ INCLUDES=$(patsubst %,-I %, $(DIRS))
 
 # Control of warnings:
 
-WARNINGS=-w +a-4-9-27
+WARNINGS=-w +a-4-9-27-70
 extraction/%.cmx: WARNINGS +=-w -20-27-32..34-39-41-44..45-60-67
 extraction/%.cmo: WARNINGS +=-w -20-27-32..34-39-41-44..45-60-67
 cparser/pre_parser.cmx: WARNINGS += -w -41

backend/IRC.ml

@@ -33,8 +33,8 @@ type node =
   { ident: int;                         (*r unique identifier *)
     typ: typ;                           (*r its type *)
     var: var;                           (*r the XTL variable it comes from *)
-    mutable regclass: int;              (*r identifier of register class *)
-    mutable accesses: int;              (*r number of defs and uses *)
+    regclass: int;                      (*r identifier of register class *)
+    accesses: int;                      (*r number of defs and uses *)
     mutable spillcost: float;           (*r estimated cost of spilling *)
     mutable adjlist: node list;         (*r all nodes it interferes with *)
     mutable degree: int;                (*r number of adjacent nodes *)
@@ -206,7 +206,7 @@ type graph = {
   varTable: (var, node) Hashtbl.t;
   mutable nextIdent: int;
   (* The adjacency set  *)
-  mutable adjSet: unit IntPairs.t;
+  adjSet: unit IntPairs.t;
   (* Low-degree, non-move-related nodes *)
   simplifyWorklist: DLinkNode.t;
   (* Low-degree, move-related nodes *)