macOS: WRKOBJDIR=/tmp/work causes some packages to fail to build

[Greg Troxel <gdt%lexort.com@localhost>]

I have WRKOBJDIR=/tmp/work, usually (avoiding it for programs that are
too piggy compared to how much RAM I have).

I tried to build sysutils/bup on macOS 13 (Ventura), with 2024Q4.  Note
that on macOS /tmp is a symlink to /private/tmp.

It failed with a complaint about not finding an include file.  But, the
clang build line had -I/tmp/private/work/sysutils.....  with a directory
that indeed had the file.

I then unset WRKOBJDIR, and the package built.  It also builds with
WRKOBJDIR=/private/tmp.

There's a known bug for gobject-type programs with a pkgsrc path that's
a symlink.   This is perhaps similar, and might be a wrapper problem.

I'm going to avoid it by not using symlinks, but I thought I'd mention
it in case anyone feels like digging in to mac/symlink/wrapper trouble.