const golang.org/x/sys/unix.CBitFieldMaskBit63

one use

	golang.org/x/sys/unix (current package)
		ztypes_linux_amd64.go#L425: 	CBitFieldMaskBit63 = 0x8000000000000000

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