ppc signal/NSIG related fix (warning fix, redefinition)

arch/powerpc/syscall_arch.h

@@ -3,8 +3,7 @@
 ((union { long long ll; long l[2]; }){ .ll = x }).l[1]
 #define __SYSCALL_LL_O(x) 0, __SYSCALL_LL_E((x))
 
-#define _NSIG 64
-#define __SYSCALL_SSLEN (_NSIG/8)
+#define __SYSCALL_SSLEN 8
 
 long (__syscall)(long, ...);