`strbasics.add` uses `copymem` when available. CT conditional
scaffolding mirrors the same from system.
Follow-up to #15951
Compile-time test for `strbasics.add` undiscarded and passes, though
pending bug #15952 is still open.
* make more standard libraries work with `nimPreviewSlimSystem`
* typo
* part two
* Delete specutils.nim
* fixes more tests
* more fixes
* fixes tests
* fixes three more tests
* add formatfloat import
* fix
* last