add Config.syntax_kind

Author: bobzhang

utils/config.mli

@@ -21,6 +21,8 @@ val version: string
 val standard_library: string
         (* The directory containing the standard libraries *)
 
+val syntax_kind : [ `ml | `reason | `rescript ] ref       
+
 val bs_only : bool ref 
 
 val standard_runtime: string

utils/config.mlp

@@ -34,6 +34,7 @@ let standard_library =
 #end
     standard_library_default
 let bs_only = ref false
+let syntax_kind = ref `ml
 let standard_runtime = "%%BYTERUN%%"
 let ccomp_type = "%%CCOMPTYPE%%"
 let c_compiler = "%%CC%%"