devel/libmsocket: enable PIC on i386, for lld

Shared objects should be built as PIC, and lld enforces this by default.
Add an i386 case to the existing set of per-arch CFLAGS, and remove the
CFLAGS_iad64 typo case.

Approved by: portmgr (lld blanket)
Sponsored by: The FreeBSD Foundation