vm/vm_mmap.c: provide extended errors for most places

[brooks]

sys/vm/vm_mmap.c

1704

Is the intent here that this is a backup message if the caller doesn't provide a more specific one?

I might use "mach vm error" for the message.

[kib]

sys/vm/vm_mmap.c

1704

Mach errors are not in errno namespace, so I do not think it is appropriate to use SET_ERROR() in the vm_map.c or vm_object.c code, which is called into by vm_mmap.c to do the actual work.

Generally SET_ERROR() should be only used in the place where the error is detected, but for Mach code it is not right.