Remove LLVMRustDIBuilderInsertDeclareAtEnd return value

The return value changed from an Instruction to a DbgRecord in
LLVM 19. As we don't actually use the result, drop the return
value entirely to support both.

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -2057,7 +2057,7 @@ extern "C" {
         AddrOpsCount: c_uint,
         DL: &'a DILocation,
         InsertAtEnd: &'a BasicBlock,
-    ) -> &'a Value;
+    );
 
     pub fn LLVMRustDIBuilderCreateEnumerator<'a>(
         Builder: &DIBuilder<'a>,