Auto merge of #88098 - Amanieu:oom_panic, r=nagisa

Implement -Z oom=panic

This PR removes the `#[rustc_allocator_nounwind]` attribute on `alloc_error_handler` which allows it to unwind with a panic instead of always aborting. This is then used to implement `-Z oom=panic` as per RFC 2116 (tracking issue #43596).

Perf and binary size tests show negligible impact.

src/test/ui/oom_unwind.rs

@@ -0,0 +1,23 @@
+// compile-flags: -Z oom=panic
+// run-pass
+// no-prefer-dynamic
+// needs-unwind
+// only-linux
+
+#![feature(bench_black_box)]
+
+use std::hint::black_box;
+use std::mem::forget;
+use std::panic::catch_unwind;
+
+fn main() {
+    let panic = catch_unwind(|| {
+        // This is guaranteed to exceed even the size of the address space
+        for _ in 0..16 {
+            // Truncates to a suitable value for both 32-bit and 64-bit targets.
+            let alloc_size = 0x1000_0000_1000_0000u64 as usize;
+            forget(black_box(vec![0u8; alloc_size]));
+        }
+    });
+    assert!(panic.is_err());
+}