RISC-V: Avoid `zext.b` #37

Job	Run time
build-macos (macos-11)	1m 57s
build-alpine (x86_64, latest-stable)	31s
build-freebsd (freebsd, x86-64, 13.2, ubuntu-22.04)	6m 44s
build-macos (macos-12)	29s
build-alpine (x86, latest-stable)	29s
build-ubuntu (ubuntu-20.04, gcc-11, g++-11)	1m 3s
build-freebsd (freebsd, arm64, 13.2, ubuntu-22.04)	6m 41s
build-macos (macos-13)	47s
build-ubuntu (ubuntu-22.04, gcc-12, g++-12)	35s
build-alpine (aarch64, latest-stable)	3m 5s
build-windows-msbuild (x64, 2019, Visual Studio 16 2019, C:\Program Files (x86)\Microsoft Visual ...	2m 13s
build-alpine (armhf, latest-stable)	2m 45s
build-windows-msys2 (gcc, g++)	3m 11s
build-windows-msbuild (x64, 2022, Visual Studio 17 2022, C:\Program Files\Microsoft Visual Studio...	1m 26s
build-alpine (armv7, latest-stable)	2m 58s
build-windows-msys2 (clang, clang++)	3m 34s
build-windows-msbuild (Win32, 2019, Visual Studio 16 2019, C:\Program Files (x86)\Microsoft Visua...	1m 30s
build-alpine (ppc64le, latest-stable)	2m 32s
build-windows-msbuild (Win32, 2022, Visual Studio 17 2022, C:\Program Files\Microsoft Visual Stud...	2m 22s
build-alpine (riscv64, edge)	2m 45s
build-alpine (s390x, latest-stable)	4m 2s
	51m 39s

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