panic-handler: Remove the no_core feature

This was introduced before `#[panic_handler]` was stable, but should no
longer be needed. Additionally, we only need it for
`builtins-test-intrinsics`, not as a dependency of `compiler-builtins`.

library/compiler-builtins/builtins-test-intrinsics/Cargo.toml

@@ -6,7 +6,7 @@ publish = false
 license = "MIT OR Apache-2.0"
 
 [dependencies]
-compiler_builtins = { path = "../compiler-builtins", features = ["compiler-builtins"]}
+compiler_builtins = { path = "../compiler-builtins", features = ["compiler-builtins"] }
 panic-handler = { path = "../crates/panic-handler" }
 
 [features]

library/compiler-builtins/compiler-builtins/Cargo.toml

@@ -24,9 +24,6 @@ core = { version = "1.0.1", optional = true, package = "rustc-std-workspace-core
 [build-dependencies]
 cc = { optional = true, version = "1.2" }
 
-[dev-dependencies]
-panic-handler = { path = "../crates/panic-handler" }
-
 [features]
 default = ["compiler-builtins"]
 

library/compiler-builtins/crates/panic-handler/src/lib.rs

@@ -1,11 +1,8 @@
 //! This is needed for tests on targets that require a `#[panic_handler]` function
 
-#![feature(no_core)]
-#![no_core]
-
-extern crate core;
+#![no_std]
 
 #[panic_handler]
-fn panic(_: &core::panic::PanicInfo) -> ! {
+fn panic(_: &core::panic::PanicInfo<'_>) -> ! {
     loop {}
 }