syscall: implement syscalls on Darwin using libSystem

There are still some references to the bare Syscall functions
in the stdlib. I will root those out in a following CL.
(This CL is big enough as it is.)
Most are in vendor directories:

cmd/vendor/golang.org/x/sys/unix/
vendor/golang_org/x/net/route/syscall.go
syscall/bpf_bsd.go
syscall/exec_unix.go
syscall/flock.go

Update #17490

Change-Id: I69ab707811530c26b652b291cadee92f5bf5c1a4
Reviewed-on: https://go-review.googlesource.com/c/141639
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Elias Naur <elias.naur@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 3 insertions, 14 deletions

diff --git a/src/syscall/exec_bsd.go b/src/syscall/exec_bsd.go
index 17ca6f06cf..30b88eba7a 100644
--- a/src/syscall/exec_bsd.go
+++ b/src/syscall/exec_bsd.go
@@ -2,12 +2,11 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd netbsd openbsd
+// +build dragonfly freebsd netbsd openbsd
 
 package syscall
 
 import (
-	"runtime"
 	"unsafe"
 )
 
@@ -43,7 +42,7 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	// Declare all variables at top in case any
 	// declarations require heap allocation (e.g., err1).
 	var (
-		r1, r2 uintptr
+		r1     uintptr
 		err1   Errno
 		nextfd int
 		i      int
@@ -62,25 +61,15 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	}
 	nextfd++
 
-	darwin := runtime.GOOS == "darwin"
-
 	// About to call fork.
 	// No more allocation or calls of non-assembly functions.
 	runtime_BeforeFork()
-	r1, r2, err1 = RawSyscall(SYS_FORK, 0, 0, 0)
+	r1, _, err1 = RawSyscall(SYS_FORK, 0, 0, 0)
 	if err1 != 0 {
 		runtime_AfterFork()
 		return 0, err1
 	}
 
-	// On Darwin:
-	//	r1 = child pid in both parent and child.
-	//	r2 = 0 in parent, 1 in child.
-	// Convert to normal Unix r1 = 0 in child.
-	if darwin && r2 == 1 {
-		r1 = 0
-	}
-
 	if r1 != 0 {
 		// parent; return PID
 		runtime_AfterFork()