Move [debug_]assert_matches to mod {core, std}::assert.

compiler/rustc_middle/src/ich/impls_syntax.rs

@@ -6,6 +6,7 @@ use crate::ich::StableHashingContext;
 use rustc_ast as ast;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_span::{BytePos, NormalizedPos, SourceFile};
+use std::assert::assert_matches;
 
 use smallvec::SmallVec;
 

compiler/rustc_mir/src/interpret/memory.rs

@@ -6,6 +6,7 @@
 //! integer. It is crucial that these operations call `check_align` *before*
 //! short-circuiting the empty case!
 
+use std::assert::assert_matches;
 use std::borrow::Cow;
 use std::collections::VecDeque;
 use std::convert::{TryFrom, TryInto};