printflike vs kprintflike

[Jeff Roberson]

I have a patch from Neal Fachan of isilon that implements a new gcc
attribute 'kprintflike' that is used in place of 'printflike' in the
kernel.  This is done to stop us from leaking kernel printf formats into
userspace.  Apparently -fformat-extensions is broken in gcc3.  This also
stops our formats from leaking into any other custom formats defined in
gcc.

This is available at http://www.chesapeake.net/~jroberson/kprintf.diff

This patch was made against 5.4 sources with some local changes.  I can
update it to 6.0, but I'm hoping some compiler guru will pick it up and
commit it.

Thanks,
Jeff