cpufeatures: fix cfg for freestanding x86 targets (#1137) #742

Job	Run time
build (1.60.0, armv7a-none-eabi)	1m 55s
build (1.60.0, thumbv7em-none-eabi)	1m 52s
build (1.60.0, wasm32-unknown-unknown)	1m 47s
build (stable, armv7a-none-eabi)	7s
build (stable, thumbv7em-none-eabi)	9s
cross (aarch64-unknown-linux-gnu, 1.60.0)	2m 20s
build (stable, wasm32-unknown-unknown)	14s
cross (aarch64-unknown-linux-gnu, stable)	34s
cross (powerpc-unknown-linux-gnu, 1.60.0)	2m 21s
cross (powerpc-unknown-linux-gnu, stable)	38s
test (i686-unknown-linux-gnu, ubuntu-latest, 1.60.0, sudo apt update && sudo apt install gcc-mult...	2m 7s
test (i686-unknown-linux-gnu, ubuntu-latest, stable, sudo apt update && sudo apt install gcc-mult...	42s
x86 (x86_64-unknown-linux-gnu, 1.72.0)	30s
test (x86_64-unknown-linux-gnu, ubuntu-latest, 1.60.0)	1m 54s
x86 (x86_64-unknown-linux-gnu, stable)	16s
test (x86_64-unknown-linux-gnu, ubuntu-latest, stable)	6s
test (x86_64-apple-darwin, macos-latest, 1.60.0)	1m 58s
test (x86_64-apple-darwin, macos-latest, stable)	20s
test (x86_64-pc-windows-msvc, windows-latest, 1.60.0)	2m 23s
test (x86_64-pc-windows-msvc, windows-latest, stable)	1m 38s
minimal-versions / minimal-versions	53s
	24m 44s

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