Revert "Repace SmallPtrSet with SmallPtrSetImpl in function arguments to avoid needing to mention the size."

Getting a weird buildbot failure that I need to investigate.

llvm-svn: 215870
diff --git a/llvm/lib/Transforms/IPO/ConstantMerge.cpp b/llvm/lib/Transforms/IPO/ConstantMerge.cpp
index 0b6ade9..23be081 100644
--- a/llvm/lib/Transforms/IPO/ConstantMerge.cpp
+++ b/llvm/lib/Transforms/IPO/ConstantMerge.cpp
@@ -66,7 +66,7 @@
 
 /// Find values that are marked as llvm.used.
 static void FindUsedValues(GlobalVariable *LLVMUsed,
-                           SmallPtrSetImpl<const GlobalValue*> &UsedValues) {
+                           SmallPtrSet<const GlobalValue*, 8> &UsedValues) {
   if (!LLVMUsed) return;
   ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());