Auto merge of #53604 - oli-obk:min_const_fn, r=Centril,varkor

Implement the `min_const_fn` feature gate

cc @RalfJung @eddyb

r? @Centril

implements the feature gate for #53555

I added a hack so the `const_fn` feature gate also enables the `min_const_fn` feature gate. This ensures that nightly users of `const_fn` don't have to touch their code at all.

The `min_const_fn` checks are run first, and if they succeeded, the `const_fn` checks are run additionally to ensure we didn't miss anything.

Author: bors

src/liballoc/lib.rs

@@ -88,7 +88,8 @@
 #![feature(box_syntax)]
 #![feature(cfg_target_has_atomic)]
 #![feature(coerce_unsized)]
-#![feature(const_fn)]
+#![cfg_attr(stage0, feature(const_fn))]
+#![cfg_attr(not(stage0), feature(min_const_fn))]
 #![feature(core_intrinsics)]
 #![feature(custom_attribute)]
 #![feature(dropck_eyepatch)]

src/liballoc/tests/lib.rs

@@ -11,7 +11,8 @@
 #![feature(allocator_api)]
 #![feature(alloc_system)]
 #![feature(box_syntax)]
-#![feature(const_fn)]
+#![cfg_attr(stage0, feature(const_fn))]
+#![cfg_attr(not(stage0), feature(min_const_fn))]
 #![feature(drain_filter)]
 #![feature(exact_size_is_empty)]
 #![feature(pattern)]