message: assert platform in time shims
diff: @@ -21,6 +21,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  let this = self.eval_context_mut();
  this.check_no_isolation("clock_gettime")?;
  + this.assert_platform("linux");
  let clk_id = this.read_scalar(clk_id_op)?.to_i32()?;
  let tp = this.deref_operand(tp_op)?;
  @@ -58,6 +59,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  let this = self.eval_context_mut();
  this.check_no_isolation("gettimeofday")?;
  + this.assert_platform("macos");
  +
  // Using tz is obsolete and should always be null
  let tz = this.read_scalar(tz_op)?.not_undef()?;
  if !this.is_null(tz)? {
  