Add support for ROOL DDE Compiler (Norcroft C)

[pzaino]

Background

@RISC-OS-Community/dev-team and others,

mUnit initial ports compiles and works fine with GCC for RISC OS. Next step is to add support for RISC OS Open Desktop Development Environment (DDE).

Use #ifdef __NORCORFT_C to patch code that doesn't compile/work with DDE or to replace included libraries

Do NOT commit directly in main, instead create your own branch or fork, make your changes and then request for a PR.

Definition of Done

• Ensure mUnit compiles on DDE
• Ensure that all tests included with the repo compile and pass with DDE
• Do not break compatibility with GCC in the process and do not change the MakefileGCC files, create new for DDE (MakefileDDE)