Introduce partial_symbol::address
    
    This introduces a partial_symbol::address method.  This method takes
    an objfile argument.  This is necessary so that we can later relocate
    a partial symbol at its point of use.  It also adds an accessor to
    compute the unrelocated value; and a method to be used for setting the
    field.
    
    Note that the new method doesn't actually perform any relocation yet.
    That will come in a subsequent patch.  However, the comments are
    written to reflect the intended, rather than the temporary, semantics.
    
    gdb/ChangeLog
    2018-07-26  Tom Tromey  <tromey@redhat.com>
    
    	* psympriv.h (struct partial_symbol) 
    	address, set_address>: New methods.
    	* psymtab.c (find_pc_sect_psymtab_closer, find_pc_sect_psymbol)
    	(fixup_psymbol_section, relocate_psymtabs): Update.
    	(print_partial_symbols): Add 'objfile' parameter.  Update.
    	(dump_psymtab, add_psymbol_to_bcache, psym_fill_psymbol_map):
    	Update.