This doesn't parse S_CONSTANT case yet, because I found that the global
variable `std::strong_ordering::equal` is a S_CONSTANT and has type of
LF_STRUCTURE which is not currently handled when creating dwarf
expression for the variable. Left a TODO for it to finish later.
This makes `lldb/test/Shell/SymbolFile/PDB/ast-restore.test` and
`lldb/test/Shell/SymbolFile/PDB/calling-conventions-x86.test` pass on
windows with native pdb plugin only.
