www/node: Clean up Makefile
- Move *_DEPENDS upward
- Sort USES
- Remove unnecessary += from MAKE_ENV
- Respect space in CC and CXX
- Update CONFLICTS_INSTALL
- Sort SHEBANG_FILES
- Remove no-op OPTIONS_DEFAULT+=${OPTIONS_DEFAULT_${OPSYS}_${OSREL:R}}
- Sort option helpers
- Take maintainership