Split the stdsimd feature into separate features #1847

Job	Run time
Check Style	21s
Automatic intrinsic verification	43s
Env Override	15s
Test (i686-unknown-linux-gnu)	3m 3s
Build Documentation	1m 51s
Test (x86_64-unknown-linux-gnu)	6m 3s
Build std_detect	1m 15s
Test (x86_64-unknown-linux-gnu-emulated)	11m 5s
Test (arm-unknown-linux-gnueabihf)	3m 0s
Test (armv7-unknown-linux-gnueabihf)	10m 48s
Test (aarch64-unknown-linux-gnu)	11m 7s
Test (riscv64gc-unknown-linux-gnu)	2m 22s
Test (powerpc64le-unknown-linux-gnu)	6m 52s
Test (s390x-unknown-linux-gnu)	2m 50s
Test (wasm32-wasi)	3m 3s
Test (i586-unknown-linux-gnu)	3m 19s
Test (nvptx64-nvidia-cuda)	39s
Test (thumbv6m-none-eabi)	17s
Test (thumbv7m-none-eabi)	20s
Test (thumbv7em-none-eabi)	17s
Test (thumbv7em-none-eabihf)	20s
Test (aarch64-apple-darwin)	1m 27s
Test (x86_64-pc-windows-msvc)	9m 13s
Test (i686-pc-windows-msvc)	5m 44s
Test (x86_64-apple-darwin, macos-11)	7m 13s
	1h 33m 27s

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