Workaround posix gaps in TI-RTOS
Workaround posix gaps in TI-RTOS

TI-RTOS-based platforms generally support posix, however there
currently are some minor gaps.  It doesn't ship with unistd.h, nor a
nano_sleep() implementation.

Signed-off-by: Chris Ring <ae1db991d8ff0ca0974d285f37a0ec52e61e0aea@ti.com>

tisb-vikram/azure-iot-sdks,tisb-vikram/azure-iot-sdks,tisb-vikram/azure-iot-sdks,tisb-vikram/azure-iot-sdks,tisb-vikram/azure-iot-sdks,tisb-vikram/azure-iot-sdks,tisb-vikram/azure-iot-sdks