Fix many problems

flake.nix

rtree-c/src/ReduceC.hs

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

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

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

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

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

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

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

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

rtree-c/test/expected/for/reduction/r11.c