Add declaration and definition case

flake.nix

rtree-c/src/ReduceC.hs

rtree-c/test/cases/small/declaration.c

rtree-c/test/cases/small/definition.c

rtree-c/test/expected/declaration/main.c

rtree-c/test/expected/declaration/reduction/r000.c

rtree-c/test/expected/declaration/reduction/r001.c

rtree-c/test/expected/declaration/reduction/r01.c

rtree-c/test/expected/declaration/reduction/r1.c

rtree-c/test/expected/definition/main.c

rtree-c/test/expected/definition/reduction/r00000.c

rtree-c/test/expected/definition/reduction/r00001.c

rtree-c/test/expected/definition/reduction/r0001.c

rtree-c/test/expected/definition/reduction/r00100.c

rtree-c/test/expected/definition/reduction/r00101.c

rtree-c/test/expected/definition/reduction/r0011.c

rtree-c/test/expected/definition/reduction/r0100.c

rtree-c/test/expected/definition/reduction/r0101.c

rtree-c/test/expected/definition/reduction/r011.c

rtree-c/test/expected/definition/reduction/r10.c