raid6/ppc: Fix build for clang

commit e213574a449f7a57d4202c1869bbc7680b6b5521 upstream.

We cannot build these files with clang as it does not allow altivec
instructions in assembly when -msoft-float is passed.

Jinsong Ji <jji@us.ibm.com> wrote:
> We currently disable Altivec/VSX support when enabling soft-float.  So
> any usage of vector builtins will break.
>
> Enable Altivec/VSX with soft-float may need quite some clean up work, so
> I guess this is currently a limitation.
>
> Removing -msoft-float will make it work (and we are lucky that no
> floating point instructions will be generated as well).

This is a workaround until the issue is resolved in clang.

Link: https://bugs.llvm.org/show_bug.cgi?id=31177
Link: https://github.com/ClangBuiltLinux/linux/issues/239


Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
[nc: Use 'ifeq ($(cc-name),clang)' instead of 'ifdef CONFIG_CC_IS_CLANG'
     because that config does not exist in 4.14; the Kconfig rewrite
     that added that config happened in 4.18]
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>