build: fix incremental building

Running `make; touch *.c; make` fails because the symlinks already
exist, and creating them again fails:
	ln: failed to create symbolic link '.../rootdev/librootdev.so.1': File exists
	make: *** [Makefile:20: .../rootdev/librootdev.so.1.0] Error 1

Add flags to force recreate/clobber the symlinks to fix.

BUG=None
TEST=`make; touch *.c; make` works

Change-Id: I67368c9446e6c59a83e1e9ca6976ea2039e93751
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/rootdev/+/5545939
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Brian Norris <briannorris@chromium.org>
1 file changed