Fix test compilation with restricted feature sets. #4502

Job	Run time
Check nightly-only targets (nightly)	23s
Check --no-default-features (nightly)	59s
Check (stable)	5m 52s
Check selected Tier 3 platforms (nightly)	5m 0s
Check (nightly)	6m 22s
Check (1.63)	9m 39s
Rustfmt	14s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 2s
Test rustix_use_experimental_asm (s390x-linux)	1m 1s
Test use-libc (ubuntu)	41s
Test use-libc (i686-linux)	1m 2s
Test (ubuntu)	49s
Test use-libc (aarch64-linux)	58s
Test (ubuntu-20.04)	48s
Test use-libc (powerpc64le-linux)	56s
Test (i686-linux)	59s
Test use-libc (riscv64-linux)	1m 4s
Test (aarch64-linux)	1m 5s
Test (powerpc64le-linux)	1m 7s
Test (riscv64-linux)	1m 17s
Test (s390x-linux)	1m 6s
Test use-libc (s390x-linux)	1m 30s
Test (arm-linux)	1m 3s
Test use-libc (arm-linux)	1m 36s
Test (ubuntu-stable)	39s
Test (i686-linux-stable)	1m 12s
Test (aarch64-linux-stable)	1m 0s
Test (riscv64-linux-stable)	1m 0s
Test (s390x-linux-stable)	1m 10s
Test (powerpc64le-linux-stable)	1m 27s
Test (arm-linux-stable)	57s
Test (ubuntu-1.63)	1m 37s
Test (i686-linux-1.63)	1m 54s
Test (aarch64-linux-1.63)	2m 38s
Test (riscv64-linux-1.63)	1m 57s
Test (s390x-linux-1.63)	1m 52s
Test (powerpc64le-linux-1.63)	1m 59s
Test (arm-linux-1.63)	2m 4s
Test (macos-latest)	28s
Test (macos-13)	51s
Test (windows)	52s
Test (windows-2019)	42s
Test (musl)	59s
	1h 11m 51s

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