After commit ef1313deafb7 attempting to build xor_vmx.c died with:

In file included from include/linux/thread_info.h:10,
                 from include/linux/preempt.h:9,
                 from arch/powerpc/lib/xor_vmx.c:22:
include/linux/types.h:29: error: both 'unsigned' and '_Bool' in declaration specifiers

Because gcc's altivec.h was #defining bool to __bool and then the kernel was
trying to typedef bool later. Out of morbid curiosity I tried copying a 2012
version of the header, and it made no difference.

diff --git a/arch/powerpc/lib/xor_vmx.c b/arch/powerpc/lib/xor_vmx.c
index e905f7c..fbb1e2c 100644
--- a/arch/powerpc/lib/xor_vmx.c
+++ b/arch/powerpc/lib/xor_vmx.c
@@ -18,6 +18,7 @@
  * Author: Anton Blanchard <anton@au.ibm.com>
  */
 #include <altivec.h>
+#undef bool
 
 #include <linux/preempt.h>
 #include <linux/export.h>