ctld: Disable -Wcast-align warnings.

clang complains about the downcasts from struct connection to struct
ctld_connection as the alignment of struct ctld_connection is higher
on 32-bit platforms. However, the warning is in this case harmless as
the downcasts are on objects originally allocated as instances of
struct ctld_connection with suitable alignment.

Reported by: npn, gjb
Fixes: 6378393308bc Add an internal libiscsiutil library.
Sponsored by: Chelsio Communications

(cherry picked from commit fa255ab1b895b4a1641206e7906086aab32b1adb)