buildman: add option -E for treating compiler warnings as errors

Add a new option '-E' for treating all compiler warnings as errors.
Eventually this will pass 'KCFLAGS=-Werror' to Kbuild.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/tools/buildman/control.py b/tools/buildman/control.py
index 73b1a14..3cac9f7 100644
--- a/tools/buildman/control.py
+++ b/tools/buildman/control.py
@@ -263,7 +263,8 @@
             incremental=options.incremental,
             per_board_out_dir=options.per_board_out_dir,
             config_only=options.config_only,
-            squash_config_y=not options.preserve_config_y)
+            squash_config_y=not options.preserve_config_y,
+            warnings_as_errors=options.warnings_as_errors)
     builder.force_config_on_failure = not options.quick
     if make_func:
         builder.do_make = make_func