Update inline assembly for x86 to support new syntax

https://github.com/rust-lang/rfcs/blob/master/text/2843-llvm-asm.md
rust-lang/rfcs#2873

Author: jlb6740

src/cpucounter.c

@@ -3,6 +3,9 @@
 uint64_t cpucounter(void)
 {
     uint64_t low, high;
-    __asm__ __volatile__ ("rdtscp" : "=a" (low), "=d" (high) : : "%ecx");
+    __asm__ __volatile__("rdtscp"
+                         : "=a"(low), "=d"(high)
+                         :
+                         : "%ecx");
     return (high << 32) | low;
 }

src/cpucounter.rs

@@ -6,7 +6,7 @@ pub(crate) struct CPUCounter;
 #[inline]
 unsafe fn cpucounter() -> u64 {
     let (low, high): (u64, u64);
-    asm!("rdtscp" :  "={eax}" (low), "={edx}" (high) : : "ecx");
+    asm!("rdtscp", out("eax") low, out("edx") high, out("ecx") _);
     (high << 32) | low
 }