This would become necessary if something failed on a platform with
16-bit int (EM_WSIZE == 2).
Remove unreachable `ret 0`. If reached, it wouldn't work to return
from _m_a_i_n.
was nearly useless; lots of fixes to qemuppc and pc86 sbrk(), which was broken;
change the pc86 console to echo output to the serial port (needed for running
tests on qemu).
