[rust] Define __rust_alloc_error_handler_should_panic_v2

rust-lang/rust#143387 made
__rust_alloc_error_handler_should_panic a function.

The new definition is needed when rolling Rust past that PR. We can
remove the old symbol afterwards.

Bug: 440481922
Change-Id: I3340edd6d96d76de14942af67939978140430424
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6875644
Commit-Queue: Arthur Eubanks <aeubanks@google.com>
Reviewed-by: Arthur Eubanks <aeubanks@google.com>
Auto-Submit: Hans Wennborg <hans@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1505162}
NOKEYCHECK=True
GitOrigin-RevId: 23d818d3c7fba4658248f17fd7b8993199242aa9

Author: zmodem

rust/allocator/lib.rs

@@ -90,7 +90,14 @@ mod both_allocators {
     #[linkage = "weak"]
     fn __rust_no_alloc_shim_is_unstable_v2() {}
 
+    #[rustc_std_internal_symbol]
+    #[linkage = "weak"]
+    fn __rust_alloc_error_handler_should_panic_v2() -> u8 {
+        0
+    }
+
     // Mangle the symbol name as rustc expects.
+    // TODO(crbug.com/440481922): Remove this after rolling past https://github.com/rust-lang/rust/pull/143387
     #[rustc_std_internal_symbol]
     #[allow(non_upper_case_globals)]
     #[linkage = "weak"]