Build failure with gcc 15

[limburgher]

https://bugzilla.redhat.com/show_bug.cgi?id=2341400

/home/builduser/rpmbuild/BUILD/supertuxkart-1.4-build/SuperTuxKart-1.4-src/lib/mcpp/system.c: In function ‘open_file’:
/home/builduser/rpmbuild/BUILD/supertuxkart-1.4-build/SuperTuxKart-1.4-src/lib/mcpp/system.c:3438:15: error: expected identifier or ‘’ before ‘true’
3438 | goto true;
| ^~~~
/home/builduser/rpmbuild/BUILD/supertuxkart-1.4-build/SuperTuxKart-1.4-src/lib/mcpp/system.c:3465:19: error: expected identifier or ‘’ before ‘false’
3465 | goto false;
| ^~~~~
/home/builduser/rpmbuild/BUILD/supertuxkart-1.4-build/SuperTuxKart-1.4-src/lib/mcpp/system.c:3470:15: error: expected identifier or ‘*’ before ‘false’
3470 | goto false;
| ^~~~~
/home/builduser/rpmbuild/BUILD/supertuxkart-1.4-build/SuperTuxKart-1.4-src/lib/mcpp/system.c:3517:1: warning: statement with no effect [-Wunused-value]
3517 | true:
| ^~~~
/home/builduser/rpmbuild/BUILD/supertuxkart-1.4-build/SuperTuxKart-1.4-src/lib/mcpp/system.c:3517:5: error: expected ‘;’ before ‘:’ token
3517 | true:
| ^
| ;