Make sure that the Attribute object represents one attribute only.

Several places were still treating the Attribute object as respresenting
multiple attributes. Those places now use the AttributeSet to represent
multiple attributes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174003 91177308-0d34-0410-b5e6-96231b3b80d8

lib/IR/Attributes.cpp

@@ -40,6 +40,9 @@ Attribute Attribute::get(LLVMContext &Context, AttrBuilder &B) {
   if (!B.hasAttributes())
     return Attribute();
 
+  assert(std::distance(B.begin(), B.end()) == 1 &&
+         "The Attribute object should represent one attribute only!");
+
   // Otherwise, build a key to look up the existing attributes.
   LLVMContextImpl *pImpl = Context.pImpl;
   FoldingSetNodeID ID;