Add feature gate for precise live drop checking

src/librustc_feature/active.rs

@@ -577,6 +577,9 @@ pub fn set(&self, features: &mut Features, span: Span) {
     /// Allows `extern "avr-interrupt" fn()` and `extern "avr-non-blocking-interrupt" fn()`.
     (active, abi_avr_interrupt, "1.45.0", Some(69664), None),
 
+    /// Be more precise when looking for live drops in a const context.
+    (active, const_precise_live_drops, "1.46.0", Some(73255), None),
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------

src/librustc_span/symbol.rs

@@ -227,6 +227,7 @@
         const_loop,
         const_mut_refs,
         const_panic,
+        const_precise_live_drops,
         const_raw_ptr_deref,
         const_raw_ptr_to_usize_cast,
         const_transmute,