[PATCH] ppc64: fix gcc 4.0 vs CONFIG_ALTIVEC

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>

arch/ppc64/Makefile

@@ -56,12 +56,19 @@ LDFLAGS_vmlinux	:= -Bstatic -e $(KERNELLOAD) -Ttext $(KERNELLOAD)
 CFLAGS		+= -msoft-float -pipe -mminimal-toc -mtraceback=none \
 		   -mcall-aixdesc
 
+GCC_VERSION     := $(call cc-version)
+GCC_BROKEN_VEC	:= $(shell if [ $(GCC_VERSION) -lt 0400 ] ; then echo "y"; fi ;)
+
 ifeq ($(CONFIG_POWER4_ONLY),y)
 ifeq ($(CONFIG_ALTIVEC),y)
+ifeq ($(GCC_BROKEN_VEC),y)
 	CFLAGS += $(call cc-option,-mcpu=970)
 else
 	CFLAGS += $(call cc-option,-mcpu=power4)
 endif
+else
+	CFLAGS += $(call cc-option,-mcpu=power4)
+endif
 else
 	CFLAGS += $(call cc-option,-mtune=power4)
 endif