[LLDB][NativePDB] Add local variables with no location info.

If we don't add local variables with no location info, when trying to print it,
lldb won't find it in the its parent DeclContext, which makes lldb to spend more
time to search all the way up in DeclContext hierarchy until found same name
variable or failed. Dwarf plugin also add local vars even if they don't have
location info.

Differential Revision: https://reviews.llvm.org/D133626