[llvm] [IR][Attribute] Add support for intersecting AttributeLists; NFC (PR #109719)

[Andreas Jonson via llvm-commits]

================
@@ -903,6 +916,98 @@ AttributeSet AttributeSet::removeAttributes(LLVMContext &C,
   return get(C, B);
 }
 
+std::optional<AttributeSet>
+AttributeSet::intersectWith(LLVMContext &C, AttributeSet Other) const {
+  if (*this == Other)
+    return *this;
+  AttrBuilder Intersected(C);
+  // Get common set of all attributes then handle each attr according to its
+  // intersect rule.
+  AttributeSet Merged = addAttributes(C, Other);
----------------
andjo403 wrote:

had been nice to have some better way to get all AttrKinds looks like a lot of extra work to make a new AttributeSet only to get a way to iterate over the AttrKinds.

https://github.com/llvm/llvm-project/pull/109719