Split bulding boot.exe and running it

This is to make development on jbuilder itself easier.

Makefile

@@ -1,8 +1,10 @@
 NAME := jbuilder
 
-# Default rule
-default:
-	ocaml build.ml
+default: boot.exe
+	./boot.exe -j 4
+
+boot.exe: bootstrap.ml
+	ocaml bootstrap.ml
 
 install:
 	opam-installer -i --prefix $(PREFIX) jbuilder.install

bootstrap.ml

@@ -307,8 +307,3 @@ let () =
           ())
   in
   if n <> 0 then exit n
-
-let () =
-  exit
-    (exec "%s"
-       (String.concat ~sep:" " ("./boot.exe" :: (List.tl (Array.to_list Sys.argv)))))

jbuilder.opam

@@ -6,7 +6,8 @@ bug-reports: "https://github.com/janestreet/jbuilder/issues"
 dev-repo: "https://github.com/janestreet/jbuilder.git"
 license: "Apache-2.0"
 build: [
-["ocaml" "build.ml" "-j" jobs]
+  ["ocaml" "bootstrap.ml"]
+  ["./boot.exe" "-j" jobs]
 ]
 available: [ ocaml-version >= "4.03.0" ]
 descr: "