Implement `select`. #4311

Job	Run time
Rustfmt	5s
Check (stable)	6m 5s
Check nightly-only targets (nightly)	22s
Check (nightly)	6m 19s
Check --no-default-features (nightly)	58s
Check (1.63)	8m 58s
Check selected Tier 3 platforms (nightly)	4m 45s
Test (ubuntu)	30s
Test rustix_use_experimental_asm (powerpc64le-linux)	54s
Test (ubuntu-20.04)	33s
Test (i686-linux)	41s
Test use-libc (ubuntu)	25s
Test (aarch64-linux)	31s
Test use-libc (i686-linux)	41s
Test (powerpc64le-linux)	28s
Test use-libc (aarch64-linux)	44s
Test (riscv64-linux)	38s
Test use-libc (powerpc64le-linux)	42s
Test (s390x-linux)	32s
Test use-libc (riscv64-linux)	33s
Test (arm-linux)	40s
Test use-libc (arm-linux)	41s
Test (ubuntu-stable)	23s
Test (i686-linux-stable)	40s
Test (aarch64-linux-stable)	42s
Test (riscv64-linux-stable)	27s
Test (s390x-linux-stable)	37s
Test (powerpc64le-linux-stable)	30s
Test (arm-linux-stable)	41s
Test (ubuntu-1.63)	38s
Test (i686-linux-1.63)	28s
Test (aarch64-linux-1.63)	41s
Test (riscv64-linux-1.63)	39s
Test (s390x-linux-1.63)	29s
Test (powerpc64le-linux-1.63)	31s
Test (arm-linux-1.63)	40s
Test (macos-latest)	22s
Test (macos-12)	37s
Test (windows)	26s
Test (windows-2019)	26s
Test (musl)	29s
	47m 11s

Provide feedback