gcc-4.0 generates altivec code implicitly when -mcpu indicates an
altivec capable CPU which is not suitable for the kernel.  However, we
used to set -mcpu=970 when CONFIG_ALTIVEC was set because a gcc-3.x bug
prevented from using -maltivec along with -mcpu=power4, thus prevented
building the RAID6 altivec code.

This patch fixes all of this by testing for the gcc version.  If 4.0 or
later, just normally use -mcpu=power4 and let the RAID6 code add
-maltivec to the few files it needs to be compiled with altivec support.
For 3.x, we still use -mcpu=970 to work around the above problem, which
is fine as 3.x will never implicitly generate altivec code.

The Makefile hackery may not be the most lovely, I welcome anybody more
skilled than me to improve it.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!