unix: generate linux/sparc64 go files using Docker

With cgo supporting sparc64 as of CL 102555 and CL 132155, the Docker
based build system can be used to generate file for linux/sparc64 as
well.

Updates golang/go#15282

Change-Id: I109e55f39d3229b24b0029c42074e439c6c54dc8
Reviewed-on: https://go-review.googlesource.com/c/102655
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/linux/mkall.go

@@ -52,8 +52,9 @@ type target struct {
 	Bits       int
 }
 
-// List of all Linux targets supported by the go compiler. sparc64 is not
-// currently supported, though a port is in progress.
+// List of all Linux targets supported by the go compiler. Currently, riscv64
+// and sparc64 are not fully supported, but there is enough support already to
+// generate Go type and error definitions.
 var targets = []target{
 	{
 		GoArch:    "386",
@@ -133,13 +134,13 @@ var targets = []target{
 		SignedChar: true,
 		Bits:       64,
 	},
-	// {
-	// 	GoArch:    "sparc64",
-	// 	LinuxArch: "sparc",
-	// 	GNUArch:   "sparc64-linux-gnu",
-	// 	BigEndian: true,
-	// 	Bits:      64,
-	// },
+	{
+		GoArch:    "sparc64",
+		LinuxArch: "sparc",
+		GNUArch:   "sparc64-linux-gnu",
+		BigEndian: true,
+		Bits:      64,
+	},
 }
 
 // ptracePairs is a list of pairs of targets that can, in some cases,
@@ -532,7 +533,7 @@ func (t *target) mksyscallFlags() (flags []string) {
 		}
 	}
 
-	// This flag menas a 64-bit value should use (even, odd)-pair.
+	// This flag means a 64-bit value should use (even, odd)-pair.
 	if t.GoArch == "arm" || (t.LinuxArch == "mips" && t.Bits == 32) {
 		flags = append(flags, "-arm")
 	}