message: use _rdtsc/__rdtscp from the core library
  instead of the x86 crate
diff: @@ -15,7 +15,8 @@ use crate::environment;
  use crate::x86::controlregs::*;
  use crate::x86::cpuid::*;
  use crate::x86::msr::*;
  -use crate::x86::time::*;
  +use core::arch::x86_64::_rdtsc as rdtsc;
  +use core::arch::x86_64::__rdtscp as rdtscp;
  use core::sync::atomic::spin_loop_hint;
  use core::{fmt, u32};
  @@ -1002,7 +1003,6 @@ pub fn get_timestamp() -> u64 {
  unsafe { TIMESTAMP_FUNCTION() }
  }
  -#[inline]
  unsafe fn get_timestamp_rdtsc() -> u64 {
  llvm_asm!("lfence" ::: "memory" : "volatile");
  let value = rdtsc();
  @@ -1010,9 +1010,9 @@ unsafe fn get_timestamp_rdtsc() -> u64 {
  value
  }
  -#[inline]
  unsafe fn get_timestamp_rdtscp() -> u64 {
  - let value = rdtscp();
  + let mut aux: u32 = 0;
  + let value = rdtscp(&mut aux as *mut u32);
  llvm_asm!("lfence" ::: "memory" : "volatile");
  value
  }
  