Rollup merge of #64007 - estebank:overlapping-patterns, r=matthewjasper

Add check for overlapping ranges to unreachable patterns lint

Fix #63987.

src/test/ui/issues/issue-13867.rs

@@ -2,7 +2,6 @@
 // Test that codegen works correctly when there are multiple refutable
 // patterns in match expression.
 
-
 enum Foo {
     FooUint(usize),
     FooNullary,

src/test/ui/issues/issue-21475.rs

@@ -1,5 +1,5 @@
 // run-pass
-#![allow(unused_imports)]
+#![allow(unused_imports, overlapping_patterns)]
 // pretty-expanded FIXME #23616
 
 use m::{START, END};

src/test/ui/issues/issue-26251.rs

@@ -1,4 +1,6 @@
 // run-pass
+#![allow(overlapping_patterns)]
+
 fn main() {
     let x = 'a';