Shen-C S42 NativeGen 0.5.0

Changes from 0.4.0:
- Native C bodies are generated for anonymous lambda forms.
- Native C bodies are generated for freeze forms.
- Closure objects carry an optional NativeFunction pointer.
- Closure application uses the native body when present and preserves the
  original interpreted body as a semantic fallback.
- All 686 named kernel defuns remain native.
- 290 anonymous closure bodies in the current S42 KLambda tree are generated
  as native C helper functions.

Focused local checks:
- (+ 1 2) => 3
- (map (/. X (+ X 1)) [1 2 3]) => [2 3 4]
- (let X 41 (thaw (freeze (+ X 1)))) => 42
