nim: 0.19.4 -> 0.20.0

- link sqlite (needed for the the stdlib sqlite module)
- update nodejs to 11.x
- use default phase order (fixes linker errors during test phase)
- substitution in ./test/async/tioselectors.nim not needed anymore
- two more tests need to be disabled
- LD=$CC workaround not needed anymore
- disable unsupported tests on aarch64
- trigger pre and post hooks
- use checkInputs instead of nativeBuildInputs
- don't override patchPhase