Reimplement some x86 intrinsics without arch-specific LLVM intrinsics #1802

Job	Run time
Check Style	20s
Env Override	31s
Build Documentation	1m 25s
Build std_detect	1m 23s
Test (i686-unknown-linux-gnu)	3m 7s
Test (x86_64-unknown-linux-gnu)	7m 12s
Test (x86_64-unknown-linux-gnu-emulated)	11m 20s
Test (arm-unknown-linux-gnueabihf)	3m 7s
Test (armv7-unknown-linux-gnueabihf)	23m 18s
Test (aarch64-unknown-linux-gnu)	29m 34s
Test (riscv64gc-unknown-linux-gnu)	2m 50s
Test (powerpc64le-unknown-linux-gnu)	7m 2s
Test (s390x-unknown-linux-gnu)	2m 55s
Test (wasm32-wasi)	3m 26s
Test (i586-unknown-linux-gnu)	3m 42s
Test (nvptx64-nvidia-cuda)	49s
Test (thumbv6m-none-eabi)	18s
Test (thumbv7m-none-eabi)	25s
Test (thumbv7em-none-eabi)	21s
Test (thumbv7em-none-eabihf)	18s
Test (aarch64-apple-darwin)	1m 55s
Test (x86_64-pc-windows-msvc)	9m 44s
Test (i686-pc-windows-msvc)	5m 34s
Test (x86_64-apple-darwin, macos-11)	8m 41s
Automatic intrinsic verification	45s
	2h 10m 2s

Provide feedback