Rollup merge of #67137 - anp:tracked-panic-internals, r=eddyb

libstd uses `core::panic::Location` where possible.

cc @eddyb

src/libstd/lib.rs

@@ -305,6 +305,7 @@
 #![feature(thread_local)]
 #![feature(toowned_clone_into)]
 #![feature(trace_macros)]
+#![feature(track_caller)]
 #![feature(try_reserve)]
 #![feature(unboxed_closures)]
 #![feature(untagged_unions)]