Do not run Soong tests for Rust on non-Linux hosts.

The Rust toolchain only supports Linux hosts, so skip Rust tests
that depend on host toolchains when building on other platforms.

Test: Tests still run on Linux hosts
Bug: 140435149
Change-Id: I298b52589ab5c6a7ec3acc4db1111596cd995d76
diff --git a/rust/rust_test.go b/rust/rust_test.go
index c68cfe7..f7c96dd 100644
--- a/rust/rust_test.go
+++ b/rust/rust_test.go
@@ -17,6 +17,7 @@
 import (
 	"io/ioutil"
 	"os"
+	"runtime"
 	"testing"
 
 	"android/soong/android"
@@ -50,6 +51,11 @@
 }
 
 func testRust(t *testing.T, bp string) *android.TestContext {
+	// TODO (b/140435149)
+	if runtime.GOOS != "linux" {
+		t.Skip("Only the Linux toolchain is supported for Rust")
+	}
+
 	t.Helper()
 	config := android.TestArchConfig(buildDir, nil)
 
@@ -66,6 +72,11 @@
 }
 
 func testRustError(t *testing.T, pattern string, bp string) {
+	// TODO (b/140435149)
+	if runtime.GOOS != "linux" {
+		t.Skip("Only the Linux toolchain is supported for Rust")
+	}
+
 	t.Helper()
 	config := android.TestArchConfig(buildDir, nil)