- Split static recipes to depend file.
- Modify makefile configurations in the block to `create_makefile`.
- Expand rust sources in extconf.rb instead of GNU make extension.
TODO: pass `CARGO_TARGET_DIR` without shell syntax.
We have name fragmentation for this feature, including "shared GC",
"modular GC", and "external GC". This commit standardizes the feature
name to "modular GC" and the implementation to "GC library".
