SDL2: fix build with gcc 14 #801

Job	Run time
what-changed	24s
commit-message	4s
pkglint	45s
build-qemu (freebsd-14.2-x86_64, freebsd, x86-64, 14.2)	2m 20s
show-vars	3s
build-qemu (openbsd-7.6-x86_64, openbsd, x86-64, 7.6)	4m 33s
build-native (ubuntu-24.04-x86_64, ubuntu-24.04)	2m 14s
build-native (macos-15-arm64, macos-15)	2m 35s
build-native (macos-13-x86_64, macos-13)	1s
build-native (cygwin-2022-x86_64, windows-2022)	1h 3m 4s
jenkins / trigger	9m 5s
jenkins / build	-1s
	1h 25m 7s

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