implement cycleclock on PPC

src/julia_internal.h

@@ -107,6 +107,12 @@ static inline uint64_t cycleclock(void)
  int64_t virtual_timer_value;
  __asm__ volatile("mrs %0, cntvct_el0" : "=r"(virtual_timer_value));
  return virtual_timer_value;
+#elif defined(_CPU_PPC64_)
+ // This returns a time-base, which is not always precisely a cycle-count.
+ // https://reviews.llvm.org/D78084
+ int64_t tb;
+ asm volatile("mfspr %0, 268" : "=r" (tb));
+ return tb;
 #else
  #warning No cycleclock() definition for your platform
  // copy from https://github.com/google/benchmark/blob/v1.5.0/src/cycleclock.h