[NFC][Utils] Eliminate DISubprogram set from BuildDebugInfoMDMap

Summary:
Previously, we'd add all SPs distinct from the cloned one into a set.
Then when cloning a local scope we'd check if it's from one of those
'distinct' SPs by checking if it's in the set. We don't need to do that.
We can just check against the cloned SP directly and drop the set.

Test Plan:
ninja check-llvm-unit check-llvm

stack-info: PR: #118625, branch: users/artempyanykh/fast-coro-upstream/6

llvm/lib/Transforms/Utils/CloneFunction.cpp

@@ -172,18 +172,15 @@ bool llvm::BuildDebugInfoMDMap(DenseMap<const Metadata *, TrackingMDRef> &MD,
     };
 
     // Avoid cloning types, compile units, and (other) subprograms.
-    SmallPtrSet<const DISubprogram *, 16> MappedToSelfSPs;
     for (DISubprogram *ISP : DIFinder.subprograms()) {
-      if (ISP != SPClonedWithinModule) {
+      if (ISP != SPClonedWithinModule)
         mapToSelfIfNew(ISP);
-        MappedToSelfSPs.insert(ISP);
-      }
     }
 
     // If a subprogram isn't going to be cloned skip its lexical blocks as well.
     for (DIScope *S : DIFinder.scopes()) {
       auto *LScope = dyn_cast<DILocalScope>(S);
-      if (LScope && MappedToSelfSPs.count(LScope->getSubprogram()))
+      if (LScope && LScope->getSubprogram() != SPClonedWithinModule)
         mapToSelfIfNew(S);
     }