Auto merge of #2914 - RalfJung:unchecked_shl, r=RalfJung

add unchecked_shl test

https://github.com/rust-lang/rust/pull/112238  made me realize that we have a test for add,sub,mul,shr but not shl. Add the missing test. Also name the existing tests more consistently.

src/tools/miri/tests/fail/intrinsics/unchecked_shl.rs

@@ -0,0 +1,8 @@
+#![feature(unchecked_math)]
+
+fn main() {
+    unsafe {
+        let _n = 1i8.unchecked_shl(8);
+        //~^ ERROR: overflowing shift by 8 in `unchecked_shl`
+    }
+}

src/tools/miri/tests/fail/intrinsics/unchecked_shl.stderr

@@ -0,0 +1,15 @@
+error: Undefined Behavior: overflowing shift by 8 in `unchecked_shl`
+  --> $DIR/unchecked_shl.rs:LL:CC
+   |
+LL |         let _n = 1i8.unchecked_shl(8);
+   |                  ^^^^^^^^^^^^^^^^^^^^ overflowing shift by 8 in `unchecked_shl`
+   |
+   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
+   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = note: BACKTRACE:
+   = note: inside `main` at $DIR/unchecked_shl.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to previous error
+

src/tools/miri/tests/fail/intrinsics/unchecked_shr.stderr

@@ -1,5 +1,5 @@
 error: Undefined Behavior: overflowing shift by 64 in `unchecked_shr`
-  --> $DIR/overflowing-unchecked-rsh.rs:LL:CC
+  --> $DIR/unchecked_shr.rs:LL:CC
    |
 LL |         let _n = 1i64.unchecked_shr(64);
    |                  ^^^^^^^^^^^^^^^^^^^^^^ overflowing shift by 64 in `unchecked_shr`
@@ -7,7 +7,7 @@ LL |         let _n = 1i64.unchecked_shr(64);
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
    = note: BACKTRACE:
-   = note: inside `main` at $DIR/overflowing-unchecked-rsh.rs:LL:CC
+   = note: inside `main` at $DIR/unchecked_shr.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace