Allow `Error::raw_os_error` to return non-`i32` codes #197

Job	Run time
Cross (sparcv9-sun-solaris)	45s
Linux x32 (x86_64-unknown-linux-gnux32)	19s
Apple Other	47s
Cross (x86_64-unknown-illumos)	24s
Tier 2 (x86_64-unknown-fuchsia)	7s
Tier 2 (x86_64-unknown-redox)	16s
Tier 3 (aarch64-kmc-solid_asp3)	21s
Tier 2 (x86_64-fortanix-unknown-sgx)	15s
ESP-IDF	24s
No Atomics	8s
Tier 3 (aarch64-unknown-nto-qnx710)	21s
Tier 3 (armv6k-nintendo-3ds)	23s
RDRAND UEFI (x86_64-unknown-uefi)	33s
RNDR	12s
Tier 3 (armv7-sony-vita-newlibeabihf)	25s
RDRAND UEFI (i686-unknown-uefi)	34s
Web no_std	26s
Tier 3 (i686-unknown-hurd-gnu)	25s
Web no_std with Atomics	26s
Tier 3 (x86_64-unknown-hermit)	25s
Web	29s
Tier 3 (x86_64-wrs-vxworks)	24s
Web with Atomics	35s
Tier 3 (x86_64-unknown-dragonfly)	25s
WasmV1 no_std	26s
Tier 3 (x86_64-unknown-haiku)	21s
WasmV1 no_std with Atomics	27s
	11m 3s

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