I'm experimentally rebuilding rawhide with the not-yet-released GCC 15 to see if anything breaks, and to help write the porting guide.  See https://fedoraproject.org/wiki/User:Dmalcolm/gcc-15

My test build with GCC 15 failed:
https://copr.fedorainfracloud.org/coprs/dmalcolm/gcc-15-smoketest-3.failed/build/8476053/

whereas my test build with GCC 14 succeeded:
https://copr.fedorainfracloud.org/coprs/dmalcolm/gcc-15-smoketest-3.failed.checker/build/8477605/

Looking at the failure logs e.g.
https://download.copr.fedorainfracloud.org/results/dmalcolm/gcc-15-smoketest-3.failed/fedora-rawhide-x86_64/08476053-SuperLUMT/builder-live.log.gz

I see:

sreadmt.c: In function 'sreadmt':
sreadmt.c:65:5: error: too many arguments to function 'dumptitle'
   65 |     dumptitle(title);
      |     ^~~~~~~~~
sreadmt.c:33:13: note: declared here
   33 | static void dumptitle();
      |             ^~~~~~~~~
sreadmt.c: At top level:
sreadmt.c:102:6: error: conflicting types for 'dumptitle'; have 'void(char *)'
  102 | void dumptitle(char *title)
      |      ^~~~~~~~~
sreadmt.c:33:13: note: previous declaration of 'dumptitle' with type 'void(void)'
   33 | static void dumptitle();
      |             ^~~~~~~~~

This is probably due to GCC 15 now defaulting to -std=gnu23, whereas GCC 14 defaulted to -std=gnu17, and C23 is stricter about function prototypes than C17.  It's probably fixable by fixing the function prototypes (or by manually adding -std=gnu17 to the C build flags)

Reproducible: Always