[verifier] Get rid of getResolverFunctionType. NFC (#102631)

With opaque pointers we can just get the pointer type for the
resolver function by using PointerType::get, making the
GlobalIFunc::getResolverFunctionType function obsolete.

Author: bjope

llvm/include/llvm/IR/GlobalIFunc.h

@@ -80,10 +80,6 @@ class GlobalIFunc final : public GlobalObject, public ilist_node<GlobalIFunc> {
         static_cast<const GlobalIFunc *>(this)->getResolverFunction());
   }
 
-  static FunctionType *getResolverFunctionType(Type *IFuncValTy) {
-    return FunctionType::get(IFuncValTy->getPointerTo(), false);
-  }
-
   static bool isValidLinkage(LinkageTypes L) {
     return isExternalLinkage(L) || isLocalLinkage(L) || isWeakLinkage(L) ||
            isLinkOnceLinkage(L);

llvm/lib/IR/Verifier.cpp

@@ -1006,9 +1006,7 @@ void Verifier::visitGlobalIFunc(const GlobalIFunc &GI) {
   Check(isa<PointerType>(Resolver->getFunctionType()->getReturnType()),
         "IFunc resolver must return a pointer", &GI);
 
-  const Type *ResolverFuncTy =
-      GlobalIFunc::getResolverFunctionType(GI.getValueType());
-  Check(ResolverTy == ResolverFuncTy->getPointerTo(GI.getAddressSpace()),
+  Check(ResolverTy == PointerType::get(Context, GI.getAddressSpace()),
         "IFunc resolver has incorrect type", &GI);
 }