[GOLD] add new method for computing a build ID

[David Miller]

From: gpike@chromium.org
Date: Wed,  3 Oct 2012 12:20:17 -0700 (PDT)

> Motivation for the change: computing a build ID is currently a
> sequential bottleneck. E.g., in the example I mentioned in my email
> yesterday, a 24.5s link was spending 5.2s on the build ID computation.

Have you tried linking with OpenSSL and using their optimized MD5 and
SHA1 variants?  I bet it makes a huge difference, some cpus even have
SHA1 and MD5 instructions.

For example, on my machine we can SHA1 at a rate of 760MB/sec and
MD5 at a rate of ~775MB/sec.