4c08780e7c
This is mostly to support Swift `let`, but I found a way to get MSVC to
emit a local `S_CONSTANT` (see test).
I saw the note about `MakeConstantLocalExpression` at
2e34fecf02/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp (L2177)
but couldn't repro with local or global (emitted as `S_LDATA32` in both
cases).