x/sys/unix: add Pipe2 function for Solaris

[andy-js]

The Pipe2 function is missing from the syscall package on Solaris. Solaris has pipe2 so it could be added.

[andy-js]

See: #40614

[tklauser]

The syscall package is frozen and no new functionality should be added to it (only bug fixes):

go/src/syscall/syscall.go

Lines 21 to 25 in 6f08e89

	// Deprecated: this package is locked down. Callers should use the
	// corresponding package in the golang.org/x/sys repository instead.
	// That is also where updates required by new systems or versions
	// should be applied. See https://golang.org/s/go1.4-syscall for more
	// information.

However, we may add Pipe2 for Solaris to the golang.org/x/sys/unix package.

[andy-js]

I'll do that. Thanks.

[tklauser]

We can leave this open to track the issue. Issues for x/sys are also in the Go issue tracker, denoted by the x/sysprefix in the subject line. Also see https://github.com/golang/sys#report-issues--send-patches

[gopherbot]

Change https://golang.org/cl/283032 mentions this issue: unix: add Pipe2 for solaris