default_alloc_error_hook: call the default hook for alloc instead of duplicating it

Author: RalfJung

library/alloc/src/alloc.rs

@@ -407,7 +407,7 @@ pub mod __alloc_error_handler {
     // called via generated `__rust_alloc_error_handler` if there is no
     // `#[alloc_error_handler]`.
     #[rustc_std_internal_symbol]
-    pub unsafe fn __rdl_oom(size: usize, _align: usize) -> ! {
+    pub fn __rdl_oom(size: usize, _align: usize) -> ! {
         extern "Rust" {
             // This symbol is emitted by rustc next to __rust_alloc_error_handler.
             // Its value depends on the -Zoom={panic,abort} compiler option.

library/std/src/alloc.rs

@@ -344,17 +344,7 @@ pub fn take_alloc_error_hook() -> fn(Layout) {
 }
 
 fn default_alloc_error_hook(layout: Layout) {
-    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;
-    }
-
-    if unsafe { __rust_alloc_error_handler_should_panic != 0 } {
-        panic!("memory allocation of {} bytes failed", layout.size());
-    } else {
-        rtprintpanic!("memory allocation of {} bytes failed\n", layout.size());
-    }
+    alloc::alloc::__alloc_error_handler::__rdl_oom(layout.size(), layout.align());
 }
 
 #[cfg(not(test))]

library/std/src/lib.rs

@@ -362,6 +362,7 @@
 // Library features (alloc):
 // tidy-alphabetical-start
 #![feature(alloc_layout_extra)]
+#![feature(alloc_internals)]
 #![feature(allocator_api)]
 #![feature(get_mut_unchecked)]
 #![feature(map_try_insert)]