[compiler] add quiet support

Author: bobzhang

parsing/location.ml

@@ -339,7 +339,9 @@ let print_warning loc ppf w =
 ;;
 
 let formatter_for_warnings = ref err_formatter;;
-let prerr_warning loc w = print_warning loc !formatter_for_warnings w;;
+let prerr_warning loc w = 
+    if not !Clflags.bs_quiet then
+      print_warning loc !formatter_for_warnings w;;
 
 let echo_eof () =
   print_newline ();

utils/clflags.ml

@@ -418,4 +418,5 @@ let dont_record_crc_unit : string option ref = ref None
 let bs_only = ref false
 let bs_gentype = ref None
 let no_assert_false = ref false
+let bs_quiet = ref false
 #end

utils/clflags.mli

@@ -242,4 +242,5 @@ val dont_record_crc_unit : string option ref
 val bs_only : bool ref (* set true on bs top*)
 val bs_gentype : string option ref
 val no_assert_false : bool ref
+val bs_quiet : bool ref 
 #end