Merge pull request #5271 from slonopotamus/cleanup-linuxisms #595

Job	Run time
build (windows/amd64)	2m 28s
build (freebsd/amd64)	2m 25s
test-windows-amd64 (containerd, ./client)	4m 15s
test-freebsd-amd64	19m 24s
test-windows-amd64 (containerd, ./cmd/buildctl)	3m 26s
test-windows-amd64 (containerd, ./worker/containerd)	2m 58s
test-windows-amd64 (containerd, ./solver)	4m 34s
test-windows-amd64 (containerd, ./frontend)	2m 10s
test-windows-amd64 (containerd, ./frontend/dockerfile)	13m 3s
test-windows-amd64 (./..., 1)	12m 3s
	1h 6m 46s

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