Also includes a related libio change.
Most of these warnings were between int or ssize_t and size_t.
In particular, various POSIX system calls like read() and write()
return ssize_t and comparing that value with the sizeof a buffer
is a common source of these warnings. Another common source is
using an int as the iterator in a for loop with the limit being
a size_t.
With the type change, some printf() specifiers needed to change also.
7f77dfae60