statfs: fixes for s390x+musl (#1835) #16

Job	Run time
rust_stable	58s
linux_native_builds (x86_64-unknown-linux-gnu)	1m 14s
minver	13s
macos	1m 35s
linux_native_builds (x86_64-unknown-linux-musl)	1m 9s
rustfmt	7s
tier3 (x86_64-unknown-dragonfly)	57s
tier3 (x86_64-unknown-openbsd)	56s
tier3 (x86_64-unknown-haiku)	55s
tier3 (i686-unknown-hurd-gnu)	56s
cross (arm-unknown-linux-gnueabi)	1m 43s
cross (armv7-unknown-linux-gnueabihf)	1m 36s
redox	32s
cross (i686-unknown-linux-gnu)	1m 40s
cross_compiling (aarch64-linux-android)	30s
cross (i686-unknown-linux-musl)	1m 43s
cross_compiling (arm-linux-androideabi)	37s
cross (mips-unknown-linux-gnu)	1m 36s
cross_compiling (armv7-linux-androideabi)	32s
cross (mips64-unknown-linux-gnuabi64)	1m 45s
cross_compiling (i686-linux-android)	29s
cross (mips64el-unknown-linux-gnuabi64)	1m 42s
cross_compiling (x86_64-linux-android)	39s
cross (mipsel-unknown-linux-gnu)	1m 39s
cross_compiling (arm-unknown-linux-musleabi)	34s
cross_compiling (x86_64-unknown-fuchsia)	26s
cross (powerpc64le-unknown-linux-gnu)	1m 41s
cross_compiling (x86_64-unknown-illumos)	26s
cross_compiling (aarch64-apple-ios, true)	26s
cross_compiling (powerpc64-unknown-linux-gnu)	33s
cross_compiling (s390x-unknown-linux-gnu)	34s
cross_compiling (x86_64-unknown-linux-gnux32)	35s
cross_compiling (x86_64-unknown-netbsd)	25s
	31m 23s

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