cpubits: change `cfg(enable_64_bit = ...)` syntax (#1426) #1238

Job	Run time
test-derive (1.85.0)	30s
test-derive (stable)	26s
x86 (x86_64-unknown-linux-gnu, stable)	20s
minimal-versions / minimal-versions	47s
build (stable, thumbv7em-none-eabi)	12s
cross (aarch64-unknown-linux-gnu, 1.85.0)	45s
x86 (x86_64-unknown-linux-gnu, 1.85.0)	23s
cross (powerpc-unknown-linux-gnu, 1.85.0)	39s
cross (powerpc-unknown-linux-gnu, stable)	47s
build (1.85.0, armv7a-none-eabi)	14s
test (x86_64-unknown-linux-gnu, ubuntu-latest, 1.85.0)	14s
build (stable, wasm32-unknown-unknown)	16s
build (1.85.0, wasm32-unknown-unknown)	14s
build (stable, armv7a-none-eabi)	18s
test (x86_64-unknown-linux-gnu, ubuntu-latest, stable)	11s
test (x86_64-pc-windows-msvc, windows-latest, 1.85.0)	36s
test (x86_64-pc-windows-msvc, windows-latest, stable)	1m 2s
test (x86_64-apple-darwin, macos-latest, 1.85.0)	20s
test (i686-unknown-linux-gnu, ubuntu-latest, stable, sudo apt update && sudo apt install gcc-mult...	32s
test (x86_64-apple-darwin, macos-latest, stable)	22s
build (1.85.0, thumbv7em-none-eabi)	15s
cross (aarch64-unknown-linux-gnu, stable)	39s
test (i686-unknown-linux-gnu, ubuntu-latest, 1.85.0, sudo apt update && sudo apt install gcc-mult...	30s
	10m 32s

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