Supports cflags for mac.

The cflags keyword in gyp doesn't work on mac. cflags should wrapped in {xcode_settings: {'OTHER_CFLAGS": cflags}}

Signed-off-by: Olli Wang <olliwang@ollix.com>
Removes unused commands and arguments.

Signed-off-by: Olli Wang <olliwang@ollix.com>
Support for adding `includes` at the root of generated GYP files.

Signed-off-by: Olli Wang <olliwang@ollix.com>