cmd/dist: skip libgcc test on arm64 and mips64

This test was always being run with external linking on these
platforms because the linker was silently forcing external linking
until CL 28971. Now it produces an error instead.

Change-Id: I794e0812711e05b150daf805dc3451507bb4cae8
Reviewed-on: https://go-review.googlesource.com/29360
Run-TryBot: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/dist/test.go

@@ -420,8 +420,10 @@ func (t *tester) registerTests() {
 			break
 		}
 
-		// Darwin/Android ARM64 fails with internal linking.
-		if (t.goos == "darwin" || t.goos == "android") && t.goarch == "arm64" {
+		// Internally linking cgo is incomplete on some architectures.
+		// https://golang.org/issue/10373
+		// https://golang.org/issue/14449
+		if t.goarch == "arm64" || t.goarch == "mips64" {
 			break
 		}