Merge pull request #4689 from crazy-max/prv-types #1

Job	Run time
build (windows/amd64)	2m 59s
build (freebsd/amd64)	2m 39s
test-freebsd-amd64	19m 53s
test-windows-amd64 (containerd, ./client)	5m 14s
test-windows-amd64 (containerd, ./cmd/buildctl)	3m 48s
test-windows-amd64 (containerd, ./worker/containerd)	2m 36s
test-windows-amd64 (containerd, ./solver)	3m 50s
test-windows-amd64 (containerd, ./frontend)	2m 30s
test-windows-amd64 (containerd, ./frontend/dockerfile)	5m 23s
test-windows-amd64 (./..., 1)	13m 25s
	1h 2m 17s

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