Auto merge of #118082 - compiler-errors:rollup-ejsc8yd, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #117828 (Avoid iterating over hashmaps in astconv)
 - #117832 (interpret: simplify handling of shifts by no longer trying to handle signed and unsigned shift amounts in the same branch)
 - #117891 (Recover `dyn` and `impl` after `for<...>`)
 - #117957 (if available use a Child's pidfd for kill/wait)
 - #117988 (Handle attempts to have multiple `cfg`d tail expressions)
 - #117994 (Ignore but do not assume region obligations from unifying headers in negative coherence)
 - #118000 (Make regionck care about placeholders in outlives components)
 - #118068 (subtree update cg_gcc 2023/11/17)

r? `@ghost`
`@rustbot` modify labels: rollup

tests/fail/intrinsics/unchecked_shl2.rs

@@ -0,0 +1,9 @@
+#![feature(core_intrinsics)]
+use std::intrinsics;
+
+fn main() {
+    unsafe {
+        let _n = intrinsics::unchecked_shl(1i8, -1);
+        //~^ ERROR: overflowing shift by -1 in `unchecked_shl`
+    }
+}

tests/fail/intrinsics/unchecked_shl2.stderr

@@ -0,0 +1,15 @@
+error: Undefined Behavior: overflowing shift by -1 in `unchecked_shl`
+  --> $DIR/unchecked_shl2.rs:LL:CC
+   |
+LL |         let _n = intrinsics::unchecked_shl(1i8, -1);
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ overflowing shift by -1 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_shl2.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to previous error
+