vendor the dependencies

There is a discrepancy of behavior of `github.com/urfave/cli` between
using go1.12 and go1.15, when the dependency is not present as vendored
source. Now this builds fine with go1.12

There are users of tar-split as a package. It is the hope that by adding
this vendored source it does not impact them depending on tar-split
itself.

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

vendor/golang.org/x/sys/unix/gccgo.go

@@ -0,0 +1,62 @@
+// Copyright 2015 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.
+
+// +build gccgo
+// +build !aix
+
+package unix
+
+import "syscall"
+
+// We can't use the gc-syntax .s files for gccgo. On the plus side
+// much of the functionality can be written directly in Go.
+
+//extern gccgoRealSyscallNoError
+func realSyscallNoError(trap, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r uintptr)
+
+//extern gccgoRealSyscall
+func realSyscall(trap, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r, errno uintptr)
+
+func SyscallNoError(trap, a1, a2, a3 uintptr) (r1, r2 uintptr) {
+	syscall.Entersyscall()
+	r := realSyscallNoError(trap, a1, a2, a3, 0, 0, 0, 0, 0, 0)
+	syscall.Exitsyscall()
+	return r, 0
+}
+
+func Syscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err syscall.Errno) {
+	syscall.Entersyscall()
+	r, errno := realSyscall(trap, a1, a2, a3, 0, 0, 0, 0, 0, 0)
+	syscall.Exitsyscall()
+	return r, 0, syscall.Errno(errno)
+}
+
+func Syscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err syscall.Errno) {
+	syscall.Entersyscall()
+	r, errno := realSyscall(trap, a1, a2, a3, a4, a5, a6, 0, 0, 0)
+	syscall.Exitsyscall()
+	return r, 0, syscall.Errno(errno)
+}
+
+func Syscall9(trap, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr, err syscall.Errno) {
+	syscall.Entersyscall()
+	r, errno := realSyscall(trap, a1, a2, a3, a4, a5, a6, a7, a8, a9)
+	syscall.Exitsyscall()
+	return r, 0, syscall.Errno(errno)
+}
+
+func RawSyscallNoError(trap, a1, a2, a3 uintptr) (r1, r2 uintptr) {
+	r := realSyscallNoError(trap, a1, a2, a3, 0, 0, 0, 0, 0, 0)
+	return r, 0
+}
+
+func RawSyscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err syscall.Errno) {
+	r, errno := realSyscall(trap, a1, a2, a3, 0, 0, 0, 0, 0, 0)
+	return r, 0, syscall.Errno(errno)
+}
+
+func RawSyscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err syscall.Errno) {
+	r, errno := realSyscall(trap, a1, a2, a3, a4, a5, a6, 0, 0, 0)
+	return r, 0, syscall.Errno(errno)
+}