systemctl: install sigbus handler (#3435)

systemctl: install sigbus handler (#3435)

This makes systemctl robust regarding journal truncation.
This is a follow-up for 2cf4172a71860c6e44

Fixes:
Core was generated by `./systemctl status systemd-journald'.
Program terminated with signal SIGBUS, Bus error.
PID 8569 - core
TID 8569:
 #0  0x00007f246cc89ed6 __memcmp_sse4_1
 #1  0x0000557ebbc6f42c journal_file_init_header
 #2  0x0000557ebbc77262 journal_file_open
 #3  0x0000557ebbc42999 file_type_wanted
 #4  0x0000557ebbc42e08 add_any_file
 #5  0x0000557ebbc43832 add_directory
 #6  0x0000557ebbc4401c add_root_directory
 #7  0x0000557ebbc442e9 add_root_directory
 #8  0x0000557ebbc446fc add_search_paths
 #9  0x0000557ebbbacb5e show_journal_by_unit
 #10 0x0000557ebbb8376d print_status_info
 #11 0x0000557ebbb86a0b show_one
 #12 0x0000557ebbb87954 show
 #13 0x0000557ebbc20b1f dispatch_verb
 #14 0x0000557ebbb90615 systemctl_main
 #15 0x0000557ebbb9159f main
 #16 0x00007f246cb3e731 __libc_start_main
 #17 0x0000557ebbb75ae9 _start