Address review comments.

Author: redstar

compiler-rt/lib/xray/xray_tsc.h

@@ -96,11 +96,11 @@ namespace __xray {
 inline bool probeRequiredCPUFeatures() XRAY_NEVER_INSTRUMENT { return true; }
 
 ALWAYS_INLINE uint64_t readTSC(uint8_t &CPU) XRAY_NEVER_INSTRUMENT {
-#if defined(__clang__)
+#if __has_builtin(__builtin_readcyclecounter)
   return __builtin_readcyclecounter();
 #else
   uint64_t Cycles;
-  asm volatile("stckf %0" : /* No output. */ : "Q"(Cycles) : "cc");
+  asm volatile("stckf %0" : : "Q"(Cycles) : "cc");
   return Cycles;
 #endif
 }