Update prebuilts to go 1.12.1

From https://ci.android.com/builds/submitted/5389456/linux/latest/go.zip

Also includes a cherry-pick of
https://github.com/golang/go/commit/ff048033e4304898245d843e79ed1a0897006c6d

Fixes: 126298064
Test: m blueprint_tools
Change-Id: I581e084f909acc0b1e3f95be6452c86c86da1bac
diff --git a/src/os/sys_aix.go b/src/os/sys_aix.go
new file mode 100644
index 0000000..53a40f2
--- /dev/null
+++ b/src/os/sys_aix.go
@@ -0,0 +1,26 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+import "syscall"
+
+// gethostname syscall cannot be used because it also returns the domain.
+// Therefore, hostname is retrieve with uname syscall and the Nodename field.
+
+func hostname() (name string, err error) {
+	var u syscall.Utsname
+	if errno := syscall.Uname(&u); errno != nil {
+		return "", NewSyscallError("uname", errno)
+	}
+	b := make([]byte, len(u.Nodename))
+	i := 0
+	for ; i < len(u.Nodename); i++ {
+		if u.Nodename[i] == 0 {
+			break
+		}
+		b[i] = byte(u.Nodename[i])
+	}
+	return string(b[:i]), nil
+}