cmd/cgo: added support for GOARCH=mips64{,le}

The actual cgo is not supported for now. This is just the cgo command.

Change-Id: I25625100ee552971f47e681b7d613cba16a2132f
Reviewed-on: https://go-review.googlesource.com/14446Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>

src/cmd/cgo/main.go

@@ -138,6 +138,8 @@ var ptrSizeMap = map[string]int64{
 	"amd64":    8,
 	"arm":      4,
 	"arm64":    8,
+	"mips64":   8,
+	"mips64le": 8,
 	"ppc64":    8,
 	"ppc64le":  8,
 	"s390":     4,
@@ -149,6 +151,8 @@ var intSizeMap = map[string]int64{
 	"amd64":    8,
 	"arm":      4,
 	"arm64":    8,
+	"mips64":   8,
+	"mips64le": 8,
 	"ppc64":    8,
 	"ppc64le":  8,
 	"s390":     4,