Retrieve a function PDB symbol correctly from nested blocks

Retrieve a function PDB symbol correctly from nested blocks

Summary:
This patch fixes a problem with retrieving a function symbol by an address in a nested block. In the current implementation of ResolveSymbolContext function it retrieves a symbol with PDB_SymType::None and then checks if found symbol's tag equals to PDB_SymType::Function. So, if nested block's symbol was found, ResolveSymbolContext does not resolve a function.

It is very simple to reproduce this. For example, in the next program

```
int main() {
  auto r = 0;
  for (auto i = 1; i <= 10; i++) {
    r += i & 1 + (i - 1) & 1 - 1;
  }

  return r;
}
```

if we will stop inside the cycle and will do a backtrace, the top element will be broken. But how we can test this? I thought to add an option to lldb-test to allow search a function by address, but the address may change when the compiler will be changed.

Patch by: Aleksandr Urakov

Reviewers: asmith, labath, zturner

Reviewed By: asmith, labath

Subscribers: stella.stamenova, llvm-commits

Differential Revision: https://reviews.llvm.org/D47939

llvm-svn: 336564