[PDB] Use the raw PDB symbol interface more accurately
[PDB] Use the raw PDB symbol interface more accurately

Summary:
This patch adds some symbol tag checks before using the `IPDBRawSymbol`
interface to improve safety and readability.

Reviewers: zturner

Reviewed By: zturner

Subscribers: lldb-commits, stella.stamenova

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D51967

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@342208 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb