Rollup merge of rust-lang#78152 - spastorino:separate-unsized-locals, r=oli-obk

Separate unsized locals

Closes rust-lang#71694

Takes over again rust-lang#72029 and rust-lang#74971

cc @RalfJung @oli-obk @pnkfelix @eddyb as they've participated in previous reviews of this PR.

Author: Dylan-DPC

alloc/src/lib.rs

@@ -130,7 +130,8 @@
 #![feature(unicode_internals)]
 #![feature(unsafe_block_in_unsafe_fn)]
 #![feature(unsize)]
-#![feature(unsized_locals)]
+#![cfg_attr(not(bootstrap), feature(unsized_fn_params))]
+#![cfg_attr(bootstrap, feature(unsized_locals))]
 #![feature(allocator_internals)]
 #![feature(slice_partition_dedup)]
 #![feature(maybe_uninit_extra, maybe_uninit_slice, maybe_uninit_uninit_array)]

core/src/lib.rs

@@ -132,7 +132,8 @@
 #![feature(transparent_unions)]
 #![feature(try_blocks)]
 #![feature(unboxed_closures)]
-#![feature(unsized_locals)]
+#![cfg_attr(not(bootstrap), feature(unsized_fn_params))]
+#![cfg_attr(bootstrap, feature(unsized_locals))]
 #![cfg_attr(bootstrap, feature(untagged_unions))]
 #![feature(unwind_attributes)]
 #![feature(variant_count)]