Add params() to FunctionType. NFC.

While at it, also use makeArrayRef in elements().

llvm-svn: 222556
diff --git a/llvm/lib/IR/LLVMContextImpl.h b/llvm/lib/IR/LLVMContextImpl.h
index f018dc7..7a298cf 100644
--- a/llvm/lib/IR/LLVMContextImpl.h
+++ b/llvm/lib/IR/LLVMContextImpl.h
@@ -148,10 +148,9 @@
     bool isVarArg;
     KeyTy(const Type* R, const ArrayRef<Type*>& P, bool V) :
       ReturnType(R), Params(P), isVarArg(V) {}
-    KeyTy(const FunctionType* FT) :
-      ReturnType(FT->getReturnType()),
-      Params(makeArrayRef(FT->param_begin(), FT->param_end())),
-      isVarArg(FT->isVarArg()) {}
+    KeyTy(const FunctionType *FT)
+        : ReturnType(FT->getReturnType()), Params(FT->params()),
+          isVarArg(FT->isVarArg()) {}
     bool operator==(const KeyTy& that) const {
       if (ReturnType != that.ReturnType)
         return false;