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

[evandro]

Summary

Rename the functions that query the optimization kind attributes.

[spatel]

LGTM

[evandro]

If anyone could give me a tip on how to avoid the review to be collapsed to just the part of whichever repo was hit first by a commit, I'd appreciate it.

lib/CodeGen/CGCall.cpp

for (StringRef Attr : CodeGenOpts.DefaultFunctionAttrs) {
     StringRef Var, Value;
     std::tie(Var, Value) = Attr.split('=');
     FuncAttrs.addAttribute(Var, Value);
   }
 }
 
 void CodeGenModule::AddDefaultFnAttrs(llvm::Function &F) {
   llvm::AttrBuilder FuncAttrs;
-  ConstructDefaultFnAttrList(F.getName(), F.optForNone(),
+  ConstructDefaultFnAttrList(F.getName(), F.hasOptNone(),
                              /* AttrOnCallsite = */ false, FuncAttrs);
   F.addAttributes(llvm::AttributeList::FunctionIndex, FuncAttrs);
 }
 
 void CodeGenModule::ConstructAttributeList(
     StringRef Name, const CGFunctionInfo &FI, CGCalleeInfo CalleeInfo,
     llvm::AttributeList &AttrList, unsigned &CallingConv, bool AttrOnCallSite) {
   llvm::AttrBuilder FuncAttrs;