Move panic handler to compiler builtins

It fits better and allows to build `compiler_builtins` independently.

Signed-off-by: Miguel Ojeda <[email protected]>

Author: ojeda

rust/compiler_builtins.rs

@@ -133,3 +133,14 @@ define_panicking_intrinsics!("`u128` should not be used", {
     __udivti3,
     __umodti3,
 });
+
+extern "C" {
+    fn rust_helper_BUG() -> !;
+}
+
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    unsafe {
+        rust_helper_BUG();
+    }
+}

rust/kernel/lib.rs

@@ -30,8 +30,6 @@
 #[cfg(not(CONFIG_RUST))]
 compile_error!("Missing kernel configuration for conditional compilation");
 
-use core::panic::PanicInfo;
-
 mod allocator;
 
 #[doc(hidden)]
@@ -130,17 +128,6 @@ impl<'a> Drop for KParamGuard<'a> {
     }
 }
 
-extern "C" {
-    fn rust_helper_BUG() -> !;
-}
-
-#[panic_handler]
-fn panic(_info: &PanicInfo) -> ! {
-    unsafe {
-        rust_helper_BUG();
-    }
-}
-
 /// Calculates the offset of a field from the beginning of the struct it belongs to.
 ///
 /// # Example