preserve uncommitted local changes in ttcn3 deps repositories

The previous Makefile rules would always overwrite uncommitted
local changes within repositories under the deps directory.

Let's assume that somebody who has local changes inside dependencies
knows what they are doing, and eliminate the risk of discarding
results of their work. Always skip repositories which contain
local changes. Only print a warning about such repositories.

Nothing changes for people who do not modify dependencies.

While testing this change, I noticed that the 'make distclean' target
was not reachable via 'make distclean', and I've fixed this as well.

Related: OS#3090
Change-Id: I0ee4ed70868b1c1efa39ad2bf200bf59ae2a2019
1 file changed