Add cfold benchmark - can't go over 5 (though Koka uses 20) because wasm runs out of stack. Not entirely sure how to handle that - I imagine we're emitting far to much on the stack frame, but also I would hope wasmtime would optimize it, and I additionally can't find a way to raise wasmtime's limit from the cli... It is worth noting that Koka notes that cfold is a benchmark that can exhaust the stack

koka_bench/cpp/CMakeLists.txt

@@ -2,7 +2,7 @@ set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED YES)
 set(CMAKE_CXX_EXTENSIONS NO)
 
-foreach (source IN ITEMS rbtree.cpp nqueens.cpp)
+foreach (source IN ITEMS rbtree.cpp nqueens.cpp cfold.cpp)
   get_filename_component(name "${source}" NAME_WE)
   set(name "cpp-${name}")