sha2

sha2: improve RISC-V Zknh backends #1206

Job	Run time
riscv32-zknh	1m 26s
riscv64-zknh	1m 37s
minimal-versions / minimal-versions	40s
set-msrv / set-msrv	2s
linux (i686-unknown-linux-gnu, 1.79.0, sudo apt update && sudo apt install gcc-multilib)	1m 8s
build (1.79.0, thumbv7em-none-eabi)	23s
linux (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	53s
macos (1.79.0)	30s
cross (1.79.0, aarch64-unknown-linux-gnu, default)	47s
build (1.79.0, wasm32-unknown-unknown)	26s
linux (x86_64-unknown-linux-gnu, 1.79.0)	48s
macos (stable)	48s
cross (1.79.0, powerpc-unknown-linux-gnu, default)	45s
build (1.79.0, loongarch64-unknown-linux-gnu)	23s
linux (x86_64-unknown-linux-gnu, stable)	36s
cross (stable, aarch64-unknown-linux-gnu, default)	38s
build (stable, thumbv7em-none-eabi)	19s
cross (stable, powerpc-unknown-linux-gnu, default)	30s
build (stable, wasm32-unknown-unknown)	36s
windows (1.79.0, x86_64-pc-windows-gnu)	1m 6s
build (stable, loongarch64-unknown-linux-gnu)	23s
windows (stable, x86_64-pc-windows-gnu)	1m 40s
	16m 24s

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