Implement Make handle_alloc_error default to panic (for no_std + liballoc)

Related: https://github.com/rust-lang/rust/issues/66741

Guarded with `#![feature(default_alloc_error_handler)]` a default
`alloc_error_handler` is called, if a custom allocator is used and no
other custom `#[alloc_error_handler]` is defined.

The panic message does not contain the size anymore, because it would
pull in the fmt machinery, which would blow up the code size
significantly.

compiler/rustc_codegen_ssa/src/traits/backend.rs

@@ -109,6 +109,7 @@ pub trait ExtraBackendMethods: CodegenBackend + WriteBackendMethods + Sized + Se
         tcx: TyCtxt<'tcx>,
         mods: &mut Self::Module,
         kind: AllocatorKind,
+        has_alloc_error_handler: bool,
     );
     /// This generates the codegen unit and returns it along with
     /// a `u64` giving an estimate of the unit's processing cost.