Noticed while searching for 'import re' instances in python code.

Rename tool directory fetched with get.py into tool's actual name. Partially breaking for development builds, but here only lwip builder needs an update to reference tools/xtensa-lx106-elf-gcc instead.
Hopefully not breaking anything else.

Updated tools/xtensa-lx106-elf -> tools/xtensa-lx106-elf-gcc in the source and docs