fcntl: adding macOs F_RDADVISE flag #1375

Job	Run time
minver	16s
macos-aarch64	3m 59s
macos	6m 3s
linux_native_builds (x86_64-unknown-linux-gnu)	4m 13s
rust_stable	1m 18s
linux_native_builds (x86_64-unknown-linux-musl)	4m 5s
rustfmt	5s
tier3 (x86_64-unknown-dragonfly)	1m 6s
tier3 (x86_64-unknown-openbsd)	1m 1s
tier3 (x86_64-unknown-haiku)	56s
redox	42s
cross_compiling (aarch64-linux-android)	37s
cross (arm-unknown-linux-gnueabi)	1m 45s
cross_compiling (arm-linux-androideabi)	37s
cross (armv7-unknown-linux-gnueabihf)	1m 54s
cross_compiling (armv7-linux-androideabi)	39s
cross (i686-unknown-linux-gnu)	1m 45s
cross_compiling (i686-linux-android)	33s
cross (i686-unknown-linux-musl)	1m 57s
cross_compiling (x86_64-linux-android)	38s
cross (mips-unknown-linux-gnu)	1m 45s
cross_compiling (arm-unknown-linux-musleabi)	38s
cross (mips64-unknown-linux-gnuabi64)	1m 55s
cross_compiling (x86_64-unknown-fuchsia)	31s
cross (mips64el-unknown-linux-gnuabi64)	1m 45s
cross_compiling (x86_64-unknown-illumos)	31s
cross (mipsel-unknown-linux-gnu)	1m 53s
cross_compiling (aarch64-apple-ios, true)	36s
cross (powerpc64le-unknown-linux-gnu)	1m 56s
cross_compiling (powerpc64-unknown-linux-gnu)	39s
cross_compiling (s390x-unknown-linux-gnu)	40s
cross_compiling (x86_64-unknown-linux-gnux32)	38s
cross_compiling (x86_64-unknown-netbsd)	34s
	48m 10s

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