Auto merge of rust-lang#117825 - fee1-dead-contrib:corefx, r=petrochenkov

Reenable effects in libcore

With rust-lang#116670, rust-lang#117531, and rust-lang#117171, I think we would be comfortable with re-enabling the effects feature for more testing in libcore.

r? `@oli-obk`
cc `@fmease`
cc rust-lang#110395

Author: bors

core/src/lib.rs

@@ -219,6 +219,7 @@
 #![feature(doc_cfg)]
 #![feature(doc_cfg_hide)]
 #![feature(doc_notable_trait)]
+#![feature(effects)]
 #![feature(exhaustive_patterns)]
 #![feature(extern_types)]
 #![feature(fundamental)]