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 on aarch64, ppc64le and s390x (though it worked on x86_64):
https://copr.fedorainfracloud.org/coprs/dmalcolm/gcc-15-smoketest-3.failed/build/8476306/

whereas my test build with GCC 14 succeeded:
https://copr.fedorainfracloud.org/coprs/dmalcolm/gcc-15-smoketest-3.failed.checker/build/8478504/

Looking at the failure logs e.g.
https://download.copr.fedorainfracloud.org/results/dmalcolm/gcc-15-smoketest-3.failed/fedora-rawhide-s390x/08476306-emacspeak/builder-live.log.gz

I see:

Unknown type:
 <integer_type 0x3ff8f2909d8 TI
    size <integer_cst 0x3ff8f282990 type <integer_type 0x3ff8f2900a8 bitsizetype> constant 128>
    unit-size <integer_cst 0x3ff8f2829a8 type <integer_type 0x3ff8f290000 sizetype> constant 16>
    align:64 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type 0x3ff8f2909d8 precision:128 min <integer_cst 0x3ff8f283540 -170141183460469231731687303715884105728> max <integer_cst 0x3ff8f283560 170141183460469231731687303715884105727>>
libgccjit.so: <built-in>:0:0: error: in tree_type_to_jit_type, at jit/dummy-frontend.cc:1305
Please submit a full bug report, with preprocessed source (by using -freport-bug).
See <http://bugzilla.redhat.com/bugzilla> for instructions.

Looks like it's hitting this code in libgccjit:

    fprintf (stderr, "Unknown type:\n");
    debug_tree (type);
    abort ();

and this is presumably a regression in GCC 15.

Reproducible: Didn't try