Small fixes for unknown-warning-option.

Using `Ignore` causes the compiler to ignore the next command line
option, we shoud use `Unit` with an empty function.

Also we need to check if there was any error during parsing the
commandline for checking if an we have an unknown warning and the
warning is set to an error.
Bug 39421

Author: bschommer

cparser/Diagnostics.ml

@@ -390,7 +390,7 @@ let warning_options =
    Exact ("-Werror"), Unit werror;
    Exact ("-Wall"), Unit wall;
    Exact ("-w"), Unit wnothing;
-   _Regexp("-Wno-.*$"), Ignore;
+   _Regexp("-Wno-.*$"), Unit (fun () -> ());
    _Regexp("-W.*$"), Self unknown_warning;
    longopt_int ("-fmax-errors") ((:=) max_error);
    Exact("-fno-diagnostics-show-option"),Unset diagnostics_show_option;

driver/Driver.ml

@@ -427,6 +427,7 @@ let _ =
     Printexc.record_backtrace true;
     Frontend.init ();
     parse_cmdline cmdline_actions;
+    Diagnostics.raise_on_errors (); (* Any error for command line arguments? *)
     DebugInit.init (); (* Initialize the debug functions *)
     if nolink () && !option_o <> None && !num_source_files >= 2 then
       fatal_error no_loc "ambiguous '-o' option (multiple source files)";