Fix some overlong lines.
Speed up updating mode_infos.

compiler/mode_info.m:
    If the new value of a field of mode_info is likely to be bit-identical
    to the old value, then test the old and new bits for equality in the
    setter, and if they are the same, do not allocate a new mode_info structure
    that is guaranteed to be the same as the old one.

    By avoiding unnecessary memory turnover, this speeds up the compiler
    by about 4%, as measured by tools/speedtest -l.