Add jsoo boot file

Signed-off-by: Rudi Grinberg <rudi.grinberg@gmail.com>

src/js_of_ocaml_rules.boot.ml

@@ -0,0 +1,8 @@
+
+let build_cm _ ~scope:_ ~dir:_ ~js_of_ocaml:_ ~src:_ ~target:_ = []
+
+let build_exe _ ~dir:_ ~js_of_ocaml:_ ~src:_ ~requires:_ = []
+
+let setup_separate_compilation_rules _ _ = ()
+
+let standard _ = []