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.

Author: bors

std/src/alloc.rs

@@ -315,7 +315,21 @@ pub fn take_alloc_error_hook() -> fn(Layout) {
 }
 
 fn default_alloc_error_hook(layout: Layout) {
-    rtprintpanic!("memory allocation of {} bytes failed\n", layout.size());
+    #[cfg(not(bootstrap))]
+    extern "Rust" {
+        // This symbol is emitted by rustc next to __rust_alloc_error_handler.
+        // Its value depends on the -Zoom={panic,abort} compiler option.
+        static __rust_alloc_error_handler_should_panic: u8;
+    }
+    #[cfg(bootstrap)]
+    let __rust_alloc_error_handler_should_panic = 0;
+
+    #[allow(unused_unsafe)]
+    if unsafe { __rust_alloc_error_handler_should_panic != 0 } {
+        panic!("memory allocation of {} bytes failed\n", layout.size());
+    } else {
+        rtprintpanic!("memory allocation of {} bytes failed\n", layout.size());
+    }
 }
 
 #[cfg(not(test))]