For the release, turn off -warn-error

Release builds should not have -warn-error so that they are resilient to addition of new warnings in newer versions of OCaml.

Makefile.extr

@@ -36,7 +36,7 @@ INCLUDES=$(patsubst %,-I %, $(DIRS))
 
 # Control of warnings:
 
-WARNINGS=-w +a-4-9-27 -strict-sequence -safe-string -warn-error +a #Deprication returns with ocaml 4.03
+WARNINGS=-w +a-4-9-27 -strict-sequence -safe-string #Deprication returns with ocaml 4.03
 extraction/%.cmx: WARNINGS +=-w -20-27-32..34-39-41-44..45
 extraction/%.cmo: WARNINGS +=-w -20-27-32..34-39-41-44..45
 cparser/pre_parser.cmx: WARNINGS += -w -41