Add example for CMake project

[elpdt852]

We should also expand to other ninja-outputting build systems and add a CMake example

[elpdt852]

Depends on #5

See:

build cmake_object_order_depends_target_util: phony || .

build CMakeFiles/util.dir/util.c.o: C_COMPILER__util_unscanned_ /home/hinshun/git/pdtpartners/nix-ninja/examples/incremental/util.c || cmake_object_order_depends_target_util
  DEP_FILE = CMakeFiles/util.dir/util.c.o.d
  OBJECT_DIR = CMakeFiles/util.dir
  OBJECT_FILE_DIR = CMakeFiles/util.dir
  TARGET_COMPILE_PDB = CMakeFiles/util.dir/util.pdb
  TARGET_PDB = libutil.pdb

[elpdt852]

Another problem is that when running nix-ninja in local mode, CMake uses absolute paths for all inputs as well which you're not allowed to create directories like /home/$USER in the sandbox:

"args": [
  "/nix/store/ii75mhh7sxl11167m1b86p0qrjsjyjmd-gcc-wrapper-14-20241116/bin/gcc    -MD -MT CMakeFiles/main.dir/main.c.o -MF CMakeFiles/main.dir/main.c.o.d -o CMakeFiles/main.dir/main.c.o -c /home/elpdt852/git/pdtpartners/nix-ninja/examples/incremental/main.c",
  "--description=Building C object CMakeFiles/main.dir/main.c.o"
],