Build

Refactor the main `cfg_if` in backends.rs #891

Job	Run time
Linux x32 (x86_64-unknown-linux-gnux32)	29s
Apple Other	1m 15s
Cross (x86_64-unknown-illumos)	36s
RNDR	26s
No Atomics	21s
Tier 2 (x86_64-unknown-fuchsia)	9s
Runtime error	18s
Tier 2 (x86_64-fortanix-unknown-sgx)	16s
Tier 2 (x86_64-unknown-redox)	1s
WasmV1 no_std	34s
Web	38s
UEFI RNG Protocol (i686-unknown-uefi)	33s
UEFI RNG Protocol (aarch64-unknown-uefi)	32s
Tier 2 (aarch64-linux-android)	1s
WasmV1 no_std with Atomics	50s
Web no_std	40s
Web with Atomics	31s
UEFI RNG Protocol (x86_64-unknown-uefi)	34s
RDRAND UEFI (i686-unknown-uefi)	40s
Build Raw Linux (riscv64gc-unknown-linux-gnu)	24s
Tier 3 (i686-unknown-hurd-gnu)	27s
Build Raw Linux (i686-unknown-linux-gnu)	28s
Tier 3 (aarch64-unknown-nto-qnx710)	23s
RDRAND UEFI (x86_64-unknown-uefi)	33s
Build Raw Linux (riscv32gc-unknown-linux-gnu)	24s
Tier 3 (x86_64-unknown-dragonfly)	24s
Tier 3 (x86_64-wrs-vxworks)	23s
Build Raw Linux (aarch64-unknown-linux-gnu)	30s
Tier 3 (x86_64-unknown-hermit)	13s
Build Raw Linux (x86_64-unknown-linux-gnu)	34s
Build Raw Linux (x86_64-unknown-linux-gnux32)	24s
Tier 3 (riscv32imc-esp-espidf)	23s
Web no_std with Atomics	32s
Build Raw Linux (s390x-unknown-linux-gnu)	22s
Tier 3 (armv7-sony-vita-newlibeabihf)	29s
Tier 3 (x86_64-unknown-haiku)	28s
Tier 3 (aarch64-kmc-solid_asp3)	28s
Tier 3 (armv6k-nintendo-3ds)	30s
Tier 3 (x86_64-unknown-linux-none)	24s
Build Raw Linux (loongarch64-unknown-linux-gnu)	22s
Build Raw Linux (arm-unknown-linux-gnueabihf)	24s
	18m 53s

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