Bump default value of WARNS for modules from 3 to 5, and
explicitly set WARNS for modules that fail with WARNS=5.

Also, turn on -Wno-missing-noreturn for clang for some files.

At the moment, among ~ 360 modules,
- 2 (lua and zfs) need WARNS=0
- 1 (solaris) needs WARNS=1
- 136 need WARNS=3 (mostly due to sign-compare)
- 4 need WARNS=4
- others can be compiled with WARNS=5

Discussed on tech-kern.

Merge the [pgoyette-compat] branch

branches: 1.3.14; 1.3.16; 1.3.18;
Reorganize SRCS lists for libcompat, compat.kmod, sysv_ipc.kmod.

- Share lists between the libcompat and module makefiles.
- Include some omitted entries in compat.kmod:
. if_43.c
. kern_sa_60.c
. kern_time_30.c
. rndpseudo_50.c
. rtsock_14.c
. rtsock_50.c
. rtsock_70.c
. uipc_syscalls_40.c
. uipc_syscalls_50.c
- Exclude a (harmless) spurious entry in sysv_ipc.kmod on LP64 systems:
. kern_ipc_10.c

Should fix broken ifconfig on modular current kernels.

ok pgoyette

branches: 1.2.2;
Merge the compat_sysv module into the sysv_ipc module - it should
never have been a separate module in the first place (my bad).

Adjust dependencies as appropriate.

branches: 1.1.2;
Create a new sysv_ipc module to contain the SYSVSHM, SYSVSEM, and
SYSVMSG options. Move associated variables out of param.c and into
the module's source file.