* The unit tests are derived from the FreeRTOS test app
in components/freertos/test_apps/freertos. They are
quite incompatible with the main test application, which
is why they have been placed under
tools/test_apps/linux_compatible/linux_freertos for now.
* Added port layer from the FreeRTOS POSIX port, added
additional port code for ESP-IDF.
* Created another hello world example using that POSIX
port in tools/test_apps.
* Removed old linux app