Build warnings

[wolfsage]

I don't know if you want to keep the build clean as you go or after. These are current warnings only seen without -DDEBUGGING:

class.c: In function ‘Perl_pp_methstart’:
class.c:200:13: warning: unused variable ‘max_fieldix’ [-Wunused-variable]
         U32 max_fieldix = (aux++)->uv;
             ^~~~~~~~~~~
class.c: In function ‘Perl_class_seal_stash’:
class.c:266:33: warning: unused parameter ‘stash’ [-Wunused-parameter]
 Perl_class_seal_stash(pTHX_ HV *stash)
                                 ^~~~~
class.c: In function ‘Perl_class_prepare_method_parse’:
class.c:286:15: warning: variable ‘padix’ set but not used [-Wunused-but-set-variable]
     PADOFFSET padix;

The seal_stash is silly but the other two are variables only used in debugging builds for sanity

[leonerd]

Not a lot that can be done about this but at least 157c58a will quiet it