Just noticed a few inconsistencies in the atomic instructions (spec) in that std/builtins.ts

• defines _s loads that don't exist for atomic ops
• misses top-level 32-bit load/store on i64.atomic
• has no definitions in std/index.d.ts
• somtimes uses formatting that is slightly off, like missing spaces

Seems this slipped through review and should be revisted, ideally with a test, to ensure that the instruction set is accurate.