DebugInfo: change the PDB UniqueId type to uint8_t

Since we type-erase the Windows GUID structure, use unsigned bytes
rather than char, which may be signed (-fsigned-char).  NFC

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290765 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed