Compile warning on Perl 5.12

[pali]

https://travis-ci.org/Dual-Life/Devel-PPPort/jobs/544798867

ppport.h: In function ‘DPPP_my_mess_sv’:
ppport.h:5308:20: warning: zero-length gnu_printf format string [-Wformat-zero-length]
         ret = mess("");
                    ^
In file included from /home/travis/perl5/perlbrew/perls/5.12/lib/5.12.5/x86_64-linux/CORE/perl.h:3418:0,
                 from RealPPPort.xs:31:
ppport.h:5314:32: warning: zero-length gnu_printf format string [-Wformat-zero-length]
         sv_catsv(basemsg, mess(""));
                                ^
/home/travis/perl5/perlbrew/perls/5.12/lib/5.12.5/x86_64-linux/CORE/sv.h:1766:48: note: in definition of macro ‘sv_catsv’
 #define sv_catsv(dsv, ssv) sv_catsv_flags(dsv, ssv, SV_GMAGIC)
                                                ^
In file included from RealPPPort.xs:142:0:
ppport.h:5318:16: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     ret = mess("");
                ^

[khwilliamson]

Does anyone have suggestions for fixing this?