[nll] librustc_codegen_llvm: change Child signature to fix error pointed out by nll

As explained by eddyb in #53221, "An &ArchiveChild doesn't point into the archive itself, it points to an owned object that itself points to the archive, and LLVMRustArchiveMemberNew copies the ArchiveChild (whereas the current signature suggests it keeps the &ArchiveChild)."

src/librustc_codegen_llvm/llvm/ffi.rs

@@ -1564,7 +1564,7 @@ extern "C" {
                                 -> LLVMRustResult;
     pub fn LLVMRustArchiveMemberNew(Filename: *const c_char,
                                     Name: *const c_char,
-                                    Child: Option<&'a ArchiveChild>)
+                                    Child: Option<&ArchiveChild<'a>>)
                                     -> &'a mut RustArchiveMember<'a>;
     pub fn LLVMRustArchiveMemberFree(Member: &'a mut RustArchiveMember<'a>);