Revert D135427 "[LTO] Make local linkage GlobalValue in non-prevailing COMDAT available_externally"

This reverts commit 89016354.

This change broke the following example and we need to check `if (GO->getComdat()->getName() == GO->getName())`
before `NonPrevailingComdats.insert(GO->getComdat());`
Revert for clarify.

```
// a.cc
template <typename T>
struct A final { virtual ~A() {} };
extern "C" void aa() { A<int> a; }
// b.cc
template <typename T>
struct A final { virtual ~A() {} };
template struct A<int>;
extern "C" void bb(A<int> *a) { delete a; }

clang -c -fpic -O0 -flto=thin a.cc && ld.lld -shared a.o b.o
```