[llvm] Add out-of-line-atomics support to GlobalISel (PR #74588)

[Matt Arsenault via llvm-commits]

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@@ -758,16 +758,32 @@ AArch64LegalizerInfo::AArch64LegalizerInfo(const AArch64Subtarget &ST)
           all(typeInSet(0, {s8, s16, s32, s64, s128}), typeIs(2, p0)));
 
   getActionDefinitionsBuilder(G_ATOMIC_CMPXCHG)
+      .libcallIf([&ST](const LegalityQuery &Query) {
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arsenm wrote:

Same for both, I would fix pre-existing deviations from legal first, then custom in a pre-commit 

https://github.com/llvm/llvm-project/pull/74588