Add const_unchecked_layout test to libcore/tests

Author: Richard-W

Diff for: src/libcore/tests/alloc.rs

@@ -0,0 +1,10 @@
+use core::alloc::Layout;
+
+#[test]
+fn const_unchecked_layout() {
+    const SIZE: usize = 0x2000;
+    const ALIGN: usize = 0x1000;
+    const LAYOUT: Layout = unsafe { Layout::from_size_align_unchecked(SIZE, ALIGN) };
+    assert_eq!(LAYOUT.size(), SIZE);
+    assert_eq!(LAYOUT.align(), ALIGN);
+}

Diff for: src/libcore/tests/lib.rs

@@ -31,10 +31,12 @@
 #![feature(slice_partition_dedup)]
 #![feature(copy_within)]
 #![feature(int_error_matching)]
+#![feature(const_fn)]
 #![warn(rust_2018_idioms)]
 
 extern crate test;
 
+mod alloc;
 mod any;
 mod array;
 mod ascii;