gcc: remove the --with-pkgversion option from the ccache hash

One of the gcc configure options that we hash for ccache is
--with-pkgversion which is set to something like Buildroot
2015.11-git-00426-ge7e7e4f - i.e., it will change with every buildroot
commit. That's obviously not wanted, so substitute this away.

Also add a \n to the printf so the output is a bit more readable.

[Peter: update documentation to match]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>