My previous efforts of using GCC to compile C and C++ applications for the Newton are now documented a bit better here. I uploaded the tools I put together so far to SourceForge. They include some Lua scripts to turn ELF executables into NCT modules, and a template makefile with the proper compiler and linker flags. The tools should be cross platform, but a cross compiler for the ARM target is still required.
Using the tools should allow compilation of C programs and linking them with the Newton libraries. Using any of the C++ classes in the Newton libraries is however quite tricky, I don’t think it will work out of the box. The reason are the different calling conventions, name mangling schemes and constructor/destructor calls.