Use thread-safe strerror_r() instead of strerror()

We have only ever fed well known error codes into strerror()
so it should never have been a problem though.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
(cherry picked from commit 4d7680c19c131175e2ec431de9a026230c968a7e)

Conflicts:
	lib/fib_lookup/lookup.c
	lib/msg.c
	lib/route/route_obj.c
	src/lib/utils.c