[gdb/testsuite] Fix xpass in gdb.python/lib-types.exp
When running gdb.python/lib-types.exp, we have an xpass:
...
(gdb) python print (str (typedef_const_typedef_class1_ref_obj.type))^M
typedef_const_typedef_class1_ref^M
(gdb) XPASS: gdb.python/lib-types.exp: \
python print (str (typedef_const_typedef_class1_ref_obj.type)) \
(PRMS gcc/55641)
...
When running the same with gcc 4.8, we have an xfail instead:
...
(gdb) python print (str (typedef_const_typedef_class1_ref_obj.type))^M
const typedef_const_typedef_class1_ref^M
(gdb) XFAIL: gdb.python/lib-types.exp: \
python print (str (typedef_const_typedef_class1_ref_obj.type)) \
(PRMS gcc/55641)
...
Fix the xpass by xfailing only for the gcc 4.8 pattern.