LateLowerGCFrame: Treat tracked stores as defs for safepoint analysis
Instead of the overzealous HasAnySafepoint check (which checked for any
safepoint anywhere in the function), have MaybeTrackStore return whether
it tracked an alloca and set FirstSafepointAfterFirstDef at the call
site. This integrates tracked stores into the existing def/safepoint
analysis, so GC frames are only created when a safepoint actually
follows the store in program order.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>