Refactor CmdToVar as a Transient Utility

[pzaino]

Summary

This task requeries some ANSI C programmign skills and knowledge of how to use SWIs directly from C. Also a minimal ARM32 Assembly knowledge is required.

Given that the uCLib project is not yet completed, CmdToVar should use a small SWIs set to handle memory and call system.

More info on how to contribute here

Definition of done

• Builds without dependecies on SharedCLibrary
• Works fine and when used to run another command the output of such command is stored in the specified Env Variable
• builds with GNU GCC and (if possible) with ROOL DDE

When completed your work please ensure you open a Pull Request to develop branch and request for a review fromt he code-review team, thanks!