[NFC] Use Aliasee to determine Type and AddrSpace in GlobalAlias::create()

[aeubanks]

Summary

As opposed to going through the Aliasee type.

For opaque pointers, we're trying to remove uses of PointerType::getElementType().

[dblaikie]

Looks good!

llvm/lib/IR/Globals.cpp

 GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
                                  LinkageTypes Linkage, const Twine &Name,
                                  GlobalValue *Aliasee) {
   return create(Ty, AddressSpace, Linkage, Name, Aliasee, Aliasee->getParent());
 }
 
 GlobalAlias *GlobalAlias::create(LinkageTypes Link, const Twine &Name,
                                  GlobalValue *Aliasee) {
-  PointerType *PTy = Aliasee->getType();
-  return create(PTy->getElementType(), PTy->getAddressSpace(), Link, Name,
+  return create(Aliasee->getValueType(), Aliasee->getAddressSpace(), Link, Name,
                 Aliasee);
 }
 
 GlobalAlias *GlobalAlias::create(const Twine &Name, GlobalValue *Aliasee) {
   return create(Aliasee->getLinkage(), Name, Aliasee);
 }
 
 void GlobalAlias::removeFromParent() {