A new infrastructure for warnings.

On the user side, coqtop and coqc take a list of warning names or categories
after -w. No prefix means activate the warning, a "-" prefix means deactivate
it, and "+" means turn the warning into an error. Special categories include
"all", and "default" which contains the warnings enabled by default.

We also provide a vernacular Set Warnings which takes the same flags as argument.

Note that coqc now prints warnings.

The name and category of a warning are printed with the warning itself.

On the developer side, Feedback.msg_warning is still accessible, but the
recommended way to print a warning is in two steps:

1) create it by:

let warn_my_warning =
  CWarnings.create ~name:"my-warning" ~category:"my-category"
    (fun args -> Pp.strbrk ...)

2) print it by:

warn_my_warning args

1 files changed, 7 insertions, 2 deletions

diff --git a/kernel/nativeconv.ml b/kernel/nativeconv.ml
index a0ff9e123..2f985e15a 100644
--- a/kernel/nativeconv.ml
+++ b/kernel/nativeconv.ml
@@ -145,11 +145,16 @@ let native_conv_gen pb sigma env univs t1 t2 =
       end
   | _ -> anomaly (Pp.str "Compilation failure") 
 
+let warn_no_native_compiler =
+  let open Pp in
+  CWarnings.create ~name:"native-compiler-disabled" ~category:"native-compiler"
+         (fun () -> strbrk "Native compiler is disabled," ++
+                      strbrk " falling back to VM conversion test.")
+
 (* Wrapper for [native_conv] above *)
 let native_conv cv_pb sigma env t1 t2 =
   if Coq_config.no_native_compiler then begin
-    let msg = "Native compiler is disabled, falling back to VM conversion test." in
-    Feedback.msg_warning (Pp.str msg);
+    warn_no_native_compiler ();
     vm_conv cv_pb env t1 t2
   end
   else