Merge pull request #3457 from yousong/bugfix/yousong-build-showdiff

build: show diffs made by checks

Makefile

@@ -126,6 +126,7 @@ fmt:
 
 fmt-check: fmt
 	@if git status --short | grep -E '^.M .*/[^.]+.go'; then \
+		git diff | cat; \
 		echo "$@: working tree modified (possibly by gofmt)" >&2 ; \
 		false ; \
 	fi
@@ -149,6 +150,7 @@ gendocgo-check: gendocgo
 goimports-check:
 	@goimports -w -local "yunion.io/x/:yunion.io/x/onecloud" pkg cmd; \
 	if git status --short | grep -E '^.M .*/[^.]+.go'; then \
+		git diff | cat; \
 		echo "$@: working tree modified (possibly by goimports)" >&2 ; \
 		echo "$@: " >&2 ; \
 		echo "$@: import spec should be grouped in order: std, 3rd-party, yunion.io/x, yunion.io/x/onecloud" >&2 ; \