Make schbench work for powerpc64 (#1)

Make schbench work for powerpc64
diff --git a/schbench.c b/schbench.c
index 023a003..bfd50ed 100644
--- a/schbench.c
+++ b/schbench.c
@@ -745,6 +745,8 @@
 #define nop __asm__ __volatile__("rep;nop": : :"memory")
 #elif defined(__aarch64__)
 #define nop __asm__ __volatile__("yield" ::: "memory")
+#elif defined(__powerpc64__)
+#define nop __asm__ __volatile__("nop": : :"memory")
 #else
 #error Unsupported architecture
 #endif