[PowerPC] Use SmallSetVector to enable deterministic build (llvm#89875)

This is to address the issue in
https://lab.llvm.org/buildbot/#/builders/54.
`SmallSetVector` interfaces as set and can be iterated in a
deterministic order.

Author: Kai Luo

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

@@ -27,7 +27,7 @@
 #include "PPCTargetStreamer.h"
 #include "TargetInfo/PowerPCTargetInfo.h"
 #include "llvm/ADT/MapVector.h"
-#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
@@ -242,7 +242,7 @@ class PPCAIXAsmPrinter : public PPCAsmPrinter {
 private:
   /// Symbols lowered from ExternalSymbolSDNodes, we will need to emit extern
   /// linkage for them in AIX.
-  SmallPtrSet<MCSymbol *, 8> ExtSymSDNodeSymbols;
+  SmallSetVector<MCSymbol *, 8> ExtSymSDNodeSymbols;
 
   /// A format indicator and unique trailing identifier to form part of the
   /// sinit/sterm function names.