GN: Use build directory for CD for scripts

tools/gn/BUILD.gn

 static_library("gn_lib") {
   sources = [
     "args.cc",
     "args.h",
     "binary_target_generator.cc",
     "binary_target_generator.h",
     "build_settings.cc",
     "build_settings.h",
     "command_args.cc",
     "command_desc.cc",
@@ skipping 23 matching lines @@
     "filesystem_utils.h",
     "functions.cc",
     "functions.h",
     "functions_target.cc",
     "function_exec_script.cc",
     "function_process_file_template.cc",
     "function_read_file.cc",
     "function_set_default_toolchain.cc",
     "function_set_defaults.cc",
     "function_template.cc",
+    "function_to_build_path.cc",
     "function_toolchain.cc",
     "function_write_file.cc",
     "group_target_generator.cc",
     "group_target_generator.h",
     "import_manager.cc",
     "import_manager.h",
     "input_conversion.cc",
     "input_conversion.h",
     "input_file.cc",
     "input_file.h",
@@ skipping 93 matching lines @@
   deps = [
     ":gn_lib",
   ]
 }
 
 test("gn_unittests") {
   sources = [
     "escape_unittest.cc",
     "file_template_unittest.cc",
     "filesystem_utils_unittest.cc",
+    "function_to_build_path_unittest.cc",
     "input_conversion_unittest.cc",
     "label_unittest.cc",
     "ninja_helper_unittest.cc",
     "parser_unittest.cc",
     "path_output_unittest.cc",
     "pattern_unittest.cc",
     "scope_per_file_provider_unittest.cc",
     "source_dir_unittest.cc",
     "string_utils_unittest.cc",
     "target_generator_unittest.cc",
     "target_manager_unittest.cc",
     "target_unittest.cc",
+    "test_with_scope.cc",
+    "test_with_scope.h",
     "tokenizer_unittest.cc",
   ]
   deps = [
     ":gn_lib",
     "//base:run_all_unittests",
     "//base:test_support_base",
     "//testing:gtest",
   ]
 }
 
 executable("generate_test_gn_data") {
   sources = [ "generate_test_gn_data.cc" ]
   deps = [ "//base" ]
 }