Add a missing #error directive (#793) #176

Job	Run time
ci (tpb, ubuntu-22.04, --pb --threads --enable-libffi, test-some-fast)	28m 21s
ci (tpb, ubuntu-22.04, --pb --threads --enable-libffi, test-some-fast)	28m 21s
ci (a6osx, macos-12)	19m 59s
ci (a6osx, macos-12)	16m 36s
ci (ta6osx, macos-12)	22m 5s
ci (ta6osx, macos-12)	22m 5s
ci (i3le, ubuntu-22.04)	11m 25s
ci (i3le, ubuntu-22.04)	11m 25s
ci (ti3le, ubuntu-22.04)	14m 32s
ci (ti3le, ubuntu-22.04)	14m 32s
ci (a6le, ubuntu-22.04)	9m 2s
ci (a6le, ubuntu-22.04)	9m 2s
ci (ta6le, ubuntu-22.04, CFLAGS+=-std=gnu89)	11m 59s
ci (ta6le, ubuntu-22.04, CFLAGS+=-std=gnu89)	11m 59s
ci (ta6le, ubuntu-22.04, reboot, -m=ta6le --force, re.boot SCHEME="chezscheme", test-some-fast)	8m 9s
ci (ta6le, ubuntu-22.04, reboot, -m=ta6le --force, re.boot SCHEME="chezscheme", test-some-fast)	8m 9s
ci (i3nt, windows-2022, vs)	11m 32s
ci (i3nt, windows-2022, vs)	11m 32s
ci (ti3nt, windows-2022, vs)	14m 48s
ci (ti3nt, windows-2022, vs)	14m 48s
ci (a6nt, windows-2022, vs)	12m 36s
ci (a6nt, windows-2022, vs)	12m 36s
ci (ta6nt, windows-2022, vs)	15m 35s
ci (ta6nt, windows-2022, vs)	15m 35s
ci (ta6nt, windows-2022, gcc, CFLAGS+=-std=gnu89)	13m 44s
ci (ta6nt, windows-2022, gcc, CFLAGS+=-std=gnu89)	13m 44s
	6h 24m 11s

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