In particular 'warning 3' was still enabled before, meaning that the
code would fail with newer OCaml compilers:
File "top.ml", line 377, characters 12-25:
Warning 3: deprecated: String.create
Use Bytes.create instead.
Since we want to continue using old OCaml for now, don't enable
this warning.
XOBJS := $(OBJS:.cmo=.cmx)
-OCAMLCFLAGS := -g -warn-error A-3
+OCAMLCFLAGS := -g -warn-error CDEFLMPSUVYZX-3
OCAMLCLIBS := -linkpkg
OCAMLOPTPACKAGES := $(OCAMLCPACKAGES)