libFuzzer_dummy_main: specify dynamic schedule chunk size as firstprivate
libFuzzer_dummy_main: specify dynamic schedule chunk size as firstprivate

GCC complains, clang does not
https://bugs.llvm.org/show_bug.cgi?id=41767
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90365
https://godbolt.org/z/CeVhEu

LebedevRI/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed