buildman: Add support for environment delta in summary

When summarising the builds, add the -U option to emit delta lines for
the default environment built into U-Boot at each commit.

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/cmdline.py b/tools/buildman/cmdline.py
index b8ddd47..e493b1a 100644
--- a/tools/buildman/cmdline.py
+++ b/tools/buildman/cmdline.py
@@ -92,6 +92,8 @@
           default=None, help='Number of builder threads to use')
     parser.add_option('-u', '--show_unknown', action='store_true',
           default=False, help='Show boards with unknown build result')
+    parser.add_option('-U', '--show-environment', action='store_true',
+          default=False, help='Show environment changes in summary')
     parser.add_option('-v', '--verbose', action='store_true',
           default=False, help='Show build results while the build progresses')
     parser.add_option('-V', '--verbose-build', action='store_true',