[GOLD] Avoid duplicate PLT stub symbols on ppc32
    
    If two objects are compiled with -fPIC or -fPIE and call the same
    function, two different PLT entries are created, one for each object,
    but the same stub symbol name is used for both.
    
    	* powerpc.cc (Stub_table::define_stub_syms): Always include object's
    	uniq_ value.