powerpc: rework sparse for lib/xor_vmx.c

Sparse doesn't seem to be passing -maltivec around properly, leading
to lots of errors:

.../include/altivec.h:34:2: error: Use the "-maltivec" flag to enable PowerPC AltiVec support
arch/powerpc/lib/xor_vmx.c:27:16: error: Expected ; at end of declaration
arch/powerpc/lib/xor_vmx.c:27:16: error: got signed
arch/powerpc/lib/xor_vmx.c:60:9: error: No right hand side of '*'-expression
arch/powerpc/lib/xor_vmx.c:60:9: error: Expected ; at end of statement
arch/powerpc/lib/xor_vmx.c:60:9: error: got v1_in
...
arch/powerpc/lib/xor_vmx.c:87:9: error: too many errors

Only include the altivec.h header for non-__CHECKER__ builds.
For builds with __CHECKER__, make up some stubs instead, as
suggested by Balbir. (The vector size of 16 is arbitrary.)
Suggested-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>
Tested-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/lib/xor_vmx.c

@@ -17,7 +17,17 @@
  *
  * Author: Anton Blanchard <anton@au.ibm.com>
  */
+
+/*
+ * Sparse (as at v0.5.0) gets very, very confused by this file.
+ * Make it a bit simpler for it.
+ */
+#if !defined(__CHECKER__)
 #include <altivec.h>
+#else
+#define vec_xor(a, b) a ^ b
+#define vector __attribute__((vector_size(16)))
+#endif
 
 #include <linux/preempt.h>
 #include <linux/export.h>