fix: add missing assembly src files to ObjCxx

Assembly files like `.S` are allowed in `srcs` of `objc_library` but we were dropping these because it was only being handled in the `else` case where we do not have Objective-C srcs.

swiftpkg/internal/swiftpkg_build_files.bzl

@@ -511,7 +511,8 @@ def _clang_target_build_file(repository_ctx, pkg_ctx, target):
                     name = child_name,
                     attrs = attrs,
                     rule_kind = rule_kind,
-                    srcs = clang_src_info.organized_srcs.cxx_srcs +
+                    srcs = clang_src_info.organized_srcs.assembly_srcs +
+                           clang_src_info.organized_srcs.cxx_srcs +
                            clang_src_info.organized_srcs.objcxx_srcs +
                            clang_src_info.organized_srcs.other_srcs +
                            res_objcxx_srcs,