Auto merge of #48851 - petrochenkov:genparattr, r=nikomatsakis

Stabilize attributes on generic parameters

Closes https://github.com/rust-lang/rust/issues/48848

diff --cc src/liballoc/lib.rs
index 51a7802540192967d0547ec09e9e7389a6bb6f79,cbbea6c19c8d6fa5b803160f88cbff9a7249d7e9..6ce2547ef6e6d1a8518d9b3835d3331234c0b94b
--- 1/src/liballoc/lib.rs
--- 2/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@@ -97,8 -97,9 +97,8 @@@
  #![feature(fmt_internals)]
  #![feature(from_ref)]
  #![feature(fundamental)]
- #![feature(generic_param_attrs)]
+ #![cfg_attr(stage0, feature(generic_param_attrs))]
  #![cfg_attr(stage0, feature(i128_type))]
 -#![feature(iter_rfold)]
  #![feature(lang_items)]
  #![feature(needs_allocator)]
  #![feature(nonzero)]