fix a gcc warning: comparison between signed and unsigned integer expressions

llvm-svn: 41972
diff --git a/llvm/lib/Support/FoldingSet.cpp b/llvm/lib/Support/FoldingSet.cpp
index 70daad9..e083f3b 100644
--- a/llvm/lib/Support/FoldingSet.cpp
+++ b/llvm/lib/Support/FoldingSet.cpp
@@ -59,7 +59,7 @@
 void FoldingSetImpl::NodeID::AddAPFloat(const APFloat& apf) {
   APInt api = apf.convertToAPInt();
   const uint64_t *p = api.getRawData();
-  for (int i=0; i<api.getNumWords(); i++)
+  for (unsigned i=0; i<api.getNumWords(); i++)
     AddInteger(*p++);
 }
 void FoldingSetImpl::NodeID::AddString(const std::string &String) {