Upstream support for XTC tools to CMake

[keithm-xmos]

This was started by @DaveAtkinsonXMOS. Here are some references:

Link to issue on CMake gitlab server:
https://gitlab.kitware.com/cmake/cmake/-/issues/12521

Initial discussion with CMake Devs on their Discord server:
https://discourse.cmake.org/t/contribution-cross-compilation-support-for-xmos-processors/3867/11

[ed-xmos]

@McCrea I wanted to make you aware of this issue created a while back. Pretty much everything the software team do now is cmake based so it does feel like it belongs in the tools.