Fixup FreeRTOS support in LEAF

[kammce]

• In config.hpp defining BOOST_LEAF_TLS_FREERTOS should also define BOOST_LEAF_NO_THREADS in order to remove the usage of std::thread in the rest of the project.
• Remove ";" from BOOST_LEAF_TLS_INDEX_TYPE macro
• Use correct FreeRTOS API for setting and reading TLS array elements