go_1_6: Fix darwin (sierra) compile, backport systime syscall fix

  patches = [

    ./remove-tools-1.5.patch

    ./creds-test.patch

    ./fix-systime-1.6.patch

    # This test checks for the wrong thing with recent tzdata. It's been fixed in master but the patch

    # actually works on old versions too.

diff --git a/src/runtime/sys_darwin_amd64.s b/src/runtime/sys_darwin_amd64.s

index e09b906ba5..fa8ff2f65c 100644

--- a/src/runtime/sys_darwin_amd64.s

+++ b/src/runtime/sys_darwin_amd64.s

@@ -157,6 +157,7 @@ systime:

 	// Fall back to system call (usually first call in this thread).

 	MOVQ	SP, DI

 	MOVQ	$0, SI

+	MOVQ	$0, DX  // required as of Sierra; Issue 16570

 	MOVL	$(0x2000000+116), AX

 	SYSCALL

 	CMPQ	AX, $0

diff --git a/src/syscall/syscall_darwin_amd64.go b/src/syscall/syscall_darwin_amd64.go

index 70b53b87f4..79083117b6 100644

--- a/src/syscall/syscall_darwin_amd64.go

+++ b/src/syscall/syscall_darwin_amd64.go

@@ -26,14 +26,21 @@ func NsecToTimeval(nsec int64) (tv Timeval) {

 }

 //sysnb	gettimeofday(tp *Timeval) (sec int64, usec int32, err error)

-func Gettimeofday(tv *Timeval) (err error) {

-	// The tv passed to gettimeofday must be non-nil

-	// but is otherwise unused.  The answers come back

-	// in the two registers.

+func Gettimeofday(tv *Timeval) error {

+	// The tv passed to gettimeofday must be non-nil.

+	// Before macOS Sierra (10.12), tv was otherwise unused and

+	// the answers came back in the two registers.

+	// As of Sierra, gettimeofday return zeros and populates

+	// tv itself.

 	sec, usec, err := gettimeofday(tv)

-	tv.Sec = sec

-	tv.Usec = usec

-	return err

+	if err != nil {

+		return err

+	}

+	if sec != 0 || usec != 0 {

+		tv.Sec = sec

+		tv.Usec = usec

+	}

+	return nil

 }

 func SetKevent(k *Kevent_t, fd, mode, flags int) {