Just a small step along the way to reduce the massive wall of spam
every time you compile.

This was done partly automagically with `cargo fix`. The rest was me
deleting or commenting out a bunch of variables. Hope nothing was
important...

https://github.com/BurntSushi/rust-memchr is supposed to be a whole
lot faster :)

Changed while loops to for - https://gitlab.redox-os.org/redox-os/relibc/issues/128

As per the comments from jD91mZM2 on the merge request.

I saw that in other parts of the `string` module iterations over `usize` were
used to increase iteration speed.  In this patch I apply the same logic to
`memcmp`.  With this change I measured a 7x speedup for `memcmp` on a ~1MB
buffer (comparing two buffers with the same content) on my machine (i7-7500U),
but I did not do any real world benchmarking for the change.  The increase in
speed comes with the tradeoff of both increased complexity and larger generated
assembly code for the function.

I tested the correctness of the implementation by generating two randomly filled
buffers and comparing the `memcmp` result of the old implementation against this
new one.

I ran the tests and currently currently three of them fail:
  - netdb (fails to run)
  - stdio/rename (fails to verify)
  - unistd/pipe (fails to verify)

They do so though regardless of this change, so I don't think they are related.

This stops configure scripts from identifying them as valid

Because we were previously converting the bytes in the format
string into Rust's char type and then printing that using the
format machinery, byte values that were not valid single-byte
UTF-8 characters failed to print correctly.  I found this while
trying to implement qsort() because the output of my test program
was mysteriously incorrect despite it working when I used glibc.