clang builds are currently failing (travis dependency issue)

- Adds the following tests
  * gcc + clang
    + IC60
    + IC60_LED
    + ICED
    + WhiteFox
    + Testing/uartOut
    + Testing/usbMuxUart
  * gcc
    + Bootloader/mk20dx128vlf5
    + Bootloader/mk20dx256vlh7