Add crc32 function to libiberty

[Ian Lance Taylor]

DJ Delorie <dj@redhat.com> writes:

> Please make sure any CRC routines added to libiberty document the
> polynomial they use.  Referencing a web site that may vanish at any
> time is too risky, despite how standard this polynomial happens to be
> at the moment.

I didn't reference the web site for the polynomial, just for background.
To be honest, I'm not sure what the polynomial is.  As the comments
explain, the algorithm I used is precisely taken from gdb, in remote.c,
and is intended to produce the same result.  Does anybody on the gdb
side know the polynomial or any other information?

Ian