RFR: JDK-8196356: Changes to m4 files don't trigger autoconf execution at build time

[Tim Bell]

Erik:

> The check for when to generate the generated configure script is not
> working quite as expected. It currently only compares timestamps if the
> local repository has any local changes in the make/autoconf directory.
> This used to make sense when we had a committed generated script, but
> now we actually do need to regenerate any time an input file is newer
> than the generated script.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8196356
>
> Webrev: http://cr.openjdk.java.net/~erikj/8196356/webrev.01/

Yes, that makes sense.  Looks good to me.

/Tim