Use black_box intrinsic in out-of-stack test

Author: tmiasko

src/test/ui/runtime/out-of-stack.rs

@@ -6,7 +6,7 @@
 // ignore-emscripten no processes
 // ignore-sgx no processes
 
-#![feature(llvm_asm)]
+#![feature(core_intrinsics)]
 #![feature(rustc_private)]
 
 #[cfg(unix)]
@@ -16,11 +16,10 @@ use std::env;
 use std::process::Command;
 use std::thread;
 
-// lifted from the test module
 // Inlining to avoid llvm turning the recursive functions into tail calls,
 // which doesn't consume stack.
 #[inline(always)]
-pub fn black_box<T>(dummy: T) { unsafe { llvm_asm!("" : : "r"(&dummy)) } }
+pub fn black_box<T>(dummy: T) { std::intrinsics::black_box(dummy); }
 
 fn silent_recurse() {
     let buf = [0u8; 1000];