Fix ABI bugs in cstring() and alloca() calls.
Fix ABI bugs in cstring() and alloca() calls.

    These calls were clobbering registers. There was also an
    off by one error in cstring() where it overwrote the top
    byte of the stack. (This didn't matter before the ABI fixes,
    since the top byte of the stack was a return address that never
    got used.)

oridb/mc,8l/myrddin,oridb/mc,oridb/mc,8l/myrddin,oridb/mc