On larger parallel WHOPR builds I find it useful to see in top which
phase a given lto1 is in.
Set the process name to lto1-wpa, lto1-ltrans, lto1-lto depending
on the current mode.
This is currently only implemented for Linux and only
using the "comm" process name, which is reported in top.
v2: Moved function to libiberty, renamed setproctitle to match
BSD. In theory it should pick up BSD's libc function for this
on a BSD system, but I haven't tested this.