Don't store AttributeSet::FunctionIndex as an int.

GCC complains: Core.cpp:1449:27: warning: overflow in implicit constant conversion [-Woverflow]
I'm not sure if that's really a problem here, but using the enum type is better
style anyways.

llvm-svn: 179696
diff --git a/llvm/lib/IR/Core.cpp b/llvm/lib/IR/Core.cpp
index 50d1aaa..c994ef2 100644
--- a/llvm/lib/IR/Core.cpp
+++ b/llvm/lib/IR/Core.cpp
@@ -1446,7 +1446,7 @@
 void LLVMAddTargetDependentFunctionAttr(LLVMValueRef Fn, const char *A,
                                         const char *V) {
   Function *Func = unwrap<Function>(Fn);
-  int Idx = AttributeSet::FunctionIndex;
+  AttributeSet::AttrIndex Idx = AttributeSet::FunctionIndex;
   AttrBuilder B;
 
   B.addAttribute(A, V);