Migrate Atomic methods from seq_cst-only to the explicit ordering surface now
that comptime value params work on generic-struct methods (workers 3c4305f /
d7a6857 / d95ba0a):
- atomic.sx: load/store take a comptime $o: Ordering (explicit, Rust-style; no
default, matching design 4.6). a.load(.acquire) -> 'load atomic .. acquire'.
- call.zig: atomicOrderingFromNode resolves a comptime-bound ordering identifier
via comptimeIntNamed (+ atomicOrderingFromTag); documents the sx-Ordering <->
IR-AtomicOrdering declaration-order invariant. The per-op validity guard fires
through the method path (a.load(.release) is a compile error).
- 1700 migrated to explicit orderings (output unchanged 7/42/43).
Suite green (715/0).
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