Remove codegen_gcc_lto_not_supported in messages.flt #2423

Job	Run time
build_system	27s
build (gcc-13.deb, --std-tests)	6m 37s
duplicates	4s
build (gcc-13.deb, --test-libcore)	13m 49s
build (gcc-13.deb, --extended-rand-tests)	8m 41s
build (gcc-13.deb, --extended-regex-example-tests)	7m 16s
build (gcc-13.deb, --extended-regex-tests)	12m 12s
build (gcc-13.deb, --test-successful-rustc --nb-parts 2 --current-part 0)	12m 18s
build (gcc-13.deb, --test-successful-rustc --nb-parts 2 --current-part 1)	11m 0s
build (gcc-13.deb, --projects)	11m 50s
build (gcc-13-without-int128.deb, --std-tests)	6m 0s
build (gcc-13-without-int128.deb, --test-libcore)	16m 26s
build (gcc-13-without-int128.deb, --extended-rand-tests)	9m 17s
build (gcc-13-without-int128.deb, --extended-regex-example-tests)	7m 12s
build (gcc-13-without-int128.deb, --extended-regex-tests)	13m 5s
build (gcc-13-without-int128.deb, --test-successful-rustc --nb-parts 2 --current-part 0)	12m 19s
build (gcc-13-without-int128.deb, --test-successful-rustc --nb-parts 2 --current-part 1)	11m 27s
build (gcc-13-without-int128.deb, --projects)	12m 46s
	2h 52m 46s

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