Always inline mem::{size_of,align_of} in debug builds

Those two are const fn and do not have any arguments. Inlining
helps reducing generated code size in debug builds.

src/libcore/mem/mod.rs

@@ -236,7 +236,7 @@ pub fn forget_unsized<T: ?Sized>(t: T) {
 /// ```
 ///
 /// [alignment]: ./fn.align_of.html
-#[inline]
+#[inline(always)]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_promotable]
 pub const fn size_of<T>() -> usize {
@@ -328,7 +328,7 @@ pub fn min_align_of_val<T: ?Sized>(val: &T) -> usize {
 ///
 /// assert_eq!(4, mem::align_of::<i32>());
 /// ```
-#[inline]
+#[inline(always)]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_promotable]
 pub const fn align_of<T>() -> usize {