unused-but-set-variable warnings lead to build failure with Apple clang 16

[fxcoudert]

Building on macOS 15 with clang 16, as part of Homebrew testing, fails due to unused-but-set-variable warnings being turned on:

/tmp/libusrsctp-20240905-96128-qgeo1n/usrsctp-0.9.5.0/usrsctplib/netinet/sctp_cc_functions.c:767:23: error: variable 't_cwnd' set but not used [-Werror,-Wunused-but-set-variable]
  767 |         uint32_t t_ssthresh, t_cwnd, incr;
      |                              ^
1 error generated.
gmake[2]: *** [usrsctplib/CMakeFiles/usrsctp.dir/build.make:135: usrsctplib/CMakeFiles/usrsctp.dir/netinet/sctp_cc_functions.c.o] Error 1
gmake[2]: *** Waiting for unfinished jobs....
/tmp/libusrsctp-20240905-96128-qgeo1n/usrsctp-0.9.5.0/usrsctplib/netinet/sctp_indata.c:3323:6: error: variable 'tot_retrans' set but not used [-Werror,-Wunused-but-set-variable]
 3323 |         int tot_retrans = 0;
      |             ^
1 error generated.
gmake[2]: *** [usrsctplib/CMakeFiles/usrsctp.dir/build.make:163: usrsctplib/CMakeFiles/usrsctp.dir/netinet/sctp_indata.c.o] Error 1
/tmp/libusrsctp-20240905-96128-qgeo1n/usrsctp-0.9.5.0/usrsctplib/netinet/sctp_pcb.c:7946:11: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
 7946 | sctp_drain()
      |           ^
      |            void
1 error generated.
gmake[2]: *** [usrsctplib/CMakeFiles/usrsctp.dir/build.make:205: usrsctplib/CMakeFiles/usrsctp.dir/netinet/sctp_pcb.c.o] Error 1
/tmp/libusrsctp-20240905-96128-qgeo1n/usrsctp-0.9.5.0/usrsctplib/netinet/sctp_output.c:9973:33: error: variable 'cnt_thru' set but not used [-Werror,-Wunused-but-set-variable]
 9973 |         int no_fragmentflg, bundle_at, cnt_thru;
      |                                        ^
/tmp/libusrsctp-20240905-96128-qgeo1n/usrsctp-0.9.5.0/usrsctplib/netinet/sctp_output.c:13419:13: error: variable 'len' set but not used [-Werror,-Wunused-but-set-variable]
 13419 |         int error, len;
       |                    ^
2 errors generated.

[fxcoudert]

Full list of errors by file:

/tmp/libusrsctp-20240905-3949-dnagdo/usrsctp-0.9.5.0/usrsctplib/user_socket.c:2860:6: error: variable 'send_count' set but not used [-Werror,-Wunused-but-set-variable]
 2860 |         int send_count;
      |             ^
/tmp/libusrsctp-20240905-3949-dnagdo/usrsctp-0.9.5.0/usrsctplib/user_socket.c:3005:6: error: variable 'send_count' set but not used [-Werror,-Wunused-but-set-variable]
 3005 |         int send_count;
      |             ^

and

/tmp/libusrsctp-20240905-3949-dnagdo/usrsctp-0.9.5.0/usrsctplib/netinet/sctp_sysctl.c:64:18: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
   64 | sctp_init_sysctls()
      |                  ^
      |                   void

and

/tmp/libusrsctp-20240905-3949-dnagdo/usrsctp-0.9.5.0/usrsctplib/netinet/sctp_pcb.c:7946:11: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
 7946 | sctp_drain()
      |           ^
      |            void

and

/tmp/libusrsctp-20240905-3949-dnagdo/usrsctp-0.9.5.0/usrsctplib/netinet/sctp_output.c:9973:33: error: variable 'cnt_thru' set but not used [-Werror,-Wunused-but-set-variable]
 9973 |         int no_fragmentflg, bundle_at, cnt_thru;
      |                                        ^
/tmp/libusrsctp-20240905-3949-dnagdo/usrsctp-0.9.5.0/usrsctplib/netinet/sctp_output.c:13419:13: error: variable 'len' set but not used [-Werror,-Wunused-but-set-variable]
 13419 |         int error, len;
       |                    ^

and

/tmp/libusrsctp-20240905-3949-dnagdo/usrsctp-0.9.5.0/usrsctplib/netinet/sctp_indata.c:3323:6: error: variable 'tot_retrans' set but not used [-Werror,-Wunused-but-set-variable]
 3323 |         int tot_retrans = 0;
      |             ^

and

/tmp/libusrsctp-20240905-3949-dnagdo/usrsctp-0.9.5.0/usrsctplib/netinet/sctp_cc_functions.c:767:23: error: variable 't_cwnd' set but not used [-Werror,-Wunused-but-set-variable]
  767 |         uint32_t t_ssthresh, t_cwnd, incr;
      |                              ^