cmov: fix truncation bug in portable implementation (#1300) #106

Job	Run time
build (1.85.0, wasm32-unknown-unknown)	17s
build (stable, thumbv7em-none-eabi)	12s
build (stable, wasm32-unknown-unknown)	14s
test (stable)	17s
test-miri (x86_64-unknown-linux-gnu)	41s
build (1.85.0, thumbv7em-none-eabi)	17s
test (1.85.0)	15s
test-careful	55s
test-miri (s390x-unknown-linux-gnu)	53s
minimal-versions / minimal-versions	24s
	4m 25s

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