Add "objfile" parameter to two partial_symtab methods
This series will cause partial symtabs to be shared across objfiles.
However, full symtabs and symbols will still be objfile-dependent, so
will be expanded separately for each objfile. So, a debug info reader
will need to know which objfile to consult when expanding a partial
symtab.
This patch adds an objfile parameter to the two relevant methods of
partial_symtab. Current implementations simply ignore them.