Added support for sequential/random madvise() on linux #168

Job	Run time
aarch64-apple-ios	35s
build (windows-2019)	1m 48s
build (ubuntu-latest)	19s
cross-windows (aarch64-pc-windows-msvc)	1m 52s
build (macos-latest)	29s
android (aarch64-linux-android)	20s
cross-windows (i686-pc-windows-msvc)	1m 36s
android (armv7-linux-androideabi)	15s
cross-linux (aarch64, aarch64-unknown-linux-gnu, aarch64-linux-gnu)	1m 10s
android (x86_64-linux-android)	14s
freebsd (13.1)	6h 0m 4s
cross-linux (arm, armv7-unknown-linux-gnueabihf, arm-linux-gnueabihf)	35s
android (i686-linux-android)	12s
freebsd (12.3)	29m 5s
cross-linux (i386, i686-unknown-linux-gnu, i686-linux-gnu)	42s
	6h 39m 16s

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