Use stdio. Don't lock to read -- we only ever rename new ccaches into
place, or overwrite endtimes to delete entries, or overwrite part of the
realm name of cc config entries.
Dropping locks around ccache iterator stepping strongly implied that we
don't expect truncation, that we only expect appends (and the
overwriting done to delete entries).
Don't unlock -- let close(2) do it, thus making fewer system calls.
Nicolas Williams
322b166c37