const golang.org/x/sys/unix.CBitFieldMaskBit50

one use

	golang.org/x/sys/unix (current package)
		ztypes_linux_amd64.go#L412: 	CBitFieldMaskBit50 = 0x4000000000000

The pages are generated with Golds v0.4.9. (GOOS=linux GOARCH=amd64)