[IR][Attribute] Add missing const def on addAllocSizeParamAttr(); NFC

Author: goldsteinn

llvm/include/llvm/IR/Attributes.h

@@ -773,7 +773,7 @@ class AttributeList {
   /// Returns a new list because attribute lists are immutable.
   [[nodiscard]] AttributeList
   addAllocSizeParamAttr(LLVMContext &C, unsigned ArgNo, unsigned ElemSizeArg,
-                        const std::optional<unsigned> &NumElemsArg);
+                        const std::optional<unsigned> &NumElemsArg) const;
 
   //===--------------------------------------------------------------------===//
   // AttributeList Accessors

llvm/lib/IR/Attributes.cpp

@@ -1608,7 +1608,7 @@ AttributeList AttributeList::addRangeRetAttr(LLVMContext &C,
 
 AttributeList AttributeList::addAllocSizeParamAttr(
     LLVMContext &C, unsigned Index, unsigned ElemSizeArg,
-    const std::optional<unsigned> &NumElemsArg) {
+    const std::optional<unsigned> &NumElemsArg) const {
   AttrBuilder B(C);
   B.addAllocSizeAttr(ElemSizeArg, NumElemsArg);
   return addParamAttributes(C, Index, B);