svr4_exec.c doesn't compile because the compiler justifiably objects to
this code from /sys/sys/exec.h:

#define STACKGAPBASE \
    ((caddr_t)(((caddr_t)PS_STRINGS - szsigcode - STACKGAPLEN) & ~ALIGNBYTES))

("Invalid arguments to binary &" is the complaint.)  Any other file using
that won't compile either, of course, but that's where the make stopped for
me...  I've added a cast to "vm_offset_t" in my sources.