[IR] Refactor attribute methods in Function class (NFC)

Rename the functions that query the optimization kind attributes.

Differential revision: https://reviews.llvm.org/D60287

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@357731 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Utils/SimplifyLibCalls.cpp

@@ -2375,7 +2375,7 @@ Value *LibCallSimplifier::optimizeFPuts(CallInst *CI, IRBuilder<> &B) {
 
   // Don't rewrite fputs to fwrite when optimising for size because fwrite
   // requires more arguments and thus extra MOVs are required.
-  if (CI->getFunction()->optForSize())
+  if (CI->getFunction()->hasOptSize())
     return nullptr;
 
   // Check if has any use