Fix no_std compilation on AIX. #3247

Job	Run time
Check nightly-only targets (nightly)	31s
Check --no-default-features (nightly)	1m 34s
Check (stable)	10m 11s
Check selected Tier 3 platforms (nightly)	6m 38s
Check (nightly)	10m 0s
Check (1.63)	15m 46s
Rustfmt	18s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 45s
Test (ubuntu)	1m 3s
Test use-libc (ubuntu)	1m 7s
Test (ubuntu-20.04)	1m 7s
Test use-libc (i686-linux)	2m 10s
Test (i686-linux)	1m 37s
Test use-libc (aarch64-linux)	1m 34s
Test (aarch64-linux)	1m 56s
Test use-libc (powerpc64le-linux)	2m 13s
Test (powerpc64le-linux)	2m 1s
Test use-libc (riscv64-linux)	1m 48s
Test (riscv64-linux)	1m 31s
Test use-libc (arm-linux)	2m 6s
Test (s390x-linux)	1m 41s
Test (arm-linux)	2m 6s
Test (ubuntu-stable)	1m 9s
Test (ubuntu-1.63)	4m 21s
Test (i686-linux-stable)	1m 36s
Test (aarch64-linux-stable)	2m 10s
Test (riscv64-linux-stable)	1m 53s
Test (s390x-linux-stable)	1m 38s
Test (powerpc64le-linux-stable)	1m 43s
Test (arm-linux-stable)	1m 39s
Test (ubuntu-1.63)	4m 8s
Test (i686-linux-1.63)	5m 51s
Test (aarch64-linux-1.63)	5m 30s
Test (riscv64-linux-1.63)	4m 35s
Test (s390x-linux-1.63)	4m 38s
Test (powerpc64le-linux-1.63)	4m 40s
Test (arm-linux-1.63)	4m 31s
Test (macos-latest)	1m 46s
Test (macos-11)	1m 24s
Test (windows)	1m 29s
Test (windows-2019)	1m 39s
	2h 7m 3s

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