Enable S8/U8_VCLAMP microkernels for RISC-V #414

Job	Run time
build-and-test / cmake-linux-x86_64	9m 49s
build-and-test / cmake-linux-aarch64	7m 15s
build-and-test / cmake-linux-armhf	7m 35s
build-and-test / cmake-linux-riscv64	5m 40s
build-and-test / cmake-linux-riscv64-rvv	5m 27s
build-and-test / cmake-windows-arm64	4m 34s
build-and-test / cmake-windows-x64	5m 53s
build-and-test / cmake-windows-x86	6m 1s
build-and-test / cmake-macos-arm64	4m 35s
build-and-test / cmake-android (arm64)	8m 41s
build-and-test / cmake-android (armv7)	6m 22s
build-and-test / cmake-android (x86)	9m 35s
build-and-test / cmake-ios-arm64	4m 30s
build-and-test / cmake-ios-x86_64	7m 13s
build-and-test / bazel-linux-x86_64-clang-18	9m 51s
build-and-test / bazel-linux-x86_64-gcc-9	5m 23s
build-and-test / bazel-linux-aarch64	9m 29s
	1h 57m 53s

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