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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@41972 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/FoldingSet.cpp b/lib/Support/FoldingSet.cpp
index 70daad9..e083f3b 100644
--- a/lib/Support/FoldingSet.cpp
+++ b/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) {