Provide default implementation of quiche_command_line_flags.h

PiperOrigin-RevId: 449066529
diff --git a/build/source_list.gni b/build/source_list.gni
index 37b047d..c09f3dd 100644
--- a/build/source_list.gni
+++ b/build/source_list.gni
@@ -1391,11 +1391,13 @@
     "src/quiche/common/platform/default/quiche_platform_impl/quiche_url_utils_impl.cc",
 ]
 default_platform_impl_tool_support_hdrs = [
+    "src/quiche/common/platform/default/quiche_platform_impl/quiche_command_line_flags_impl.h",
     "src/quiche/common/platform/default/quiche_platform_impl/quiche_file_utils_impl.h",
     "src/quiche/common/platform/default/quiche_platform_impl/quiche_stream_buffer_allocator_impl.h",
     "src/quiche/common/platform/default/quiche_platform_impl/quiche_system_event_loop_impl.h",
 ]
 default_platform_impl_tool_support_srcs = [
+    "src/quiche/common/platform/default/quiche_platform_impl/quiche_command_line_flags_impl.cc",
     "src/quiche/common/platform/default/quiche_platform_impl/quiche_file_utils_impl.cc",
 ]
 default_platform_impl_test_support_hdrs = [