Add `mlockall` and `munlockall` (#872) #3429

Job	Run time
Check --no-default-features (nightly)	1m 8s
Check selected Tier 3 platforms (nightly)	5m 29s
Check (stable)	8m 57s
Check (nightly)	10m 36s
Check nightly-only targets (nightly)	31s
Rustfmt	16s
Check (1.63)	15m 59s
Test (ubuntu)	1m 12s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 35s
Test (ubuntu-20.04)	1m 2s
Test use-libc (ubuntu)	1m 16s
Test (i686-linux)	1m 28s
Test use-libc (i686-linux)	1m 36s
Test (aarch64-linux)	1m 30s
Test use-libc (aarch64-linux)	2m 17s
Test (powerpc64le-linux)	2m 3s
Test use-libc (powerpc64le-linux)	1m 32s
Test (riscv64-linux)	1m 54s
Test use-libc (riscv64-linux)	2m 1s
Test (s390x-linux)	1m 43s
Test use-libc (arm-linux)	1m 41s
Test (arm-linux)	1m 56s
Test (ubuntu-stable)	1m 5s
Test (i686-linux-stable)	1m 46s
Test (aarch64-linux-stable)	1m 41s
Test (riscv64-linux-stable)	2m 6s
Test (s390x-linux-stable)	1m 35s
Test (powerpc64le-linux-stable)	1m 37s
Test (arm-linux-stable)	1m 37s
Test (ubuntu-1.63)	5m 50s
Test (i686-linux-1.63)	6m 22s
Test (aarch64-linux-1.63)	6m 58s
Test (riscv64-linux-1.63)	6m 20s
Test (s390x-linux-1.63)	5m 40s
Test (powerpc64le-linux-1.63)	6m 9s
Test (arm-linux-1.63)	5m 23s
Test (macos-latest)	1m 46s
Test (macos-11)	1m 27s
Test (windows)	1m 24s
Test (windows-2019)	1m 22s
	2h 7m 50s

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