2.3.4 doesnt compile on FreeBSD 11.2 using clang

[Chris]

extract below, this has already been reported a while back but still
no new patch, so this email is to serve as a reminder, if someone
manually fixes it for the ports tree, I dont consider that a fix,
ideally we need this fixed in the source code, as not everyone will
install it from ports.

Chris

"clang40 -DHAVE_CONFIG_H -I. -I../..  -I../../src/lib
-I../../src/lib-dns -I../../src/lib-test -I../../src/lib-settings
-I../../src/lib-ssl-iostream -DPKG_RUNDIR=\""/var/run/dovecot"\"
-DPKG_STATEDIR=\""/var/lib/dovecot"\" -DSYSCONFDIR=\""/etc/dovecot"\"
-DBINDIR=\""/usr/bin"\" -I/usr/local/include  -std=gnu99
-fdiagnostics-color -Wl,-rpath=/usr/local/llvm40/lib -O2 -pipe
-march=native -fno-strict-aliasing -fstack-protector-strong
-U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -Wall -W -Wmissing-prototypes
-Wmissing-declarations -Wpointer-arith -Wchar-subscripts -Wformat=2
-Wbad-function-cast -Wno-duplicate-decl-specifier -Wstrict-aliasing=2
-I/usr/local/include   -MT test-event-stats.o -MD -MP -MF
.deps/test-event-stats.Tpo -c -o test-event-stats.o test-event-stats.c
clang-4.0: warning: -Wl,-rpath=/usr/local/llvm40/lib: 'linker' input
unused [-Wunused-command-line-argument]
test-event-stats.c:101:8: warning: implicit declaration of function
'kill' is invalid in C99 [-Wimplicit-function-declaration]
        (void)kill(stats_pid, SIGKILL);
              ^
test-event-stats.c:101:24: error: use of undeclared identifier 'SIGKILL'
        (void)kill(stats_pid, SIGKILL);
                              ^
1 warning and 1 error generated.
gmake[2]: *** [Makefile:656: test-event-stats.o] Error 1
gmake[2]: Leaving directory
'/usr/local/directadmin/custombuild/dovecot-2.3.4/src/lib-master'
gmake[1]: *** [Makefile:565: install-recursive] Error 1
gmake[1]: Leaving directory
'/usr/local/directadmin/custombuild/dovecot-2.3.4/src'
gmake: *** [Makefile:683: install-recursive] Error 1"