mail/mess822: Fix build with Clang 18

./load install hier.o auto_home.o strerr.a substdio.a stralloc.a alloc.a open.a error.a str.a
./install
install: fatal: unable to mkdir /wrkdirs/usr/ports/mail/mess822/work/stage/usr/local: no error

• Error code 111

Stop.
make: stopped in /wrkdirs/usr/ports/mail/mess822/work/mess822-0.58

• Error code 1

https://lists.freebsd.org/archives/freebsd-pkg-fallout/2024-June/608592.html

MFH: 2024Q3 (build fix)
Reported by: pkg-fallout