Expose ProductVariables from TestConfig

In preparation for unexporting ProductVariables, explicitly return a
pointer to the structure from TestConfig / TestArchConfig.

Bug: 76168832
Test: m blueprint_tools
Change-Id: Iccfb4c912f8e0ee3f620cc1ee00f0cdc5cba7735
diff --git a/cc/cc_test.go b/cc/cc_test.go
index d3ac43b..10c1aba 100644
--- a/cc/cc_test.go
+++ b/cc/cc_test.go
@@ -188,8 +188,8 @@
 func testCc(t *testing.T, bp string) *android.TestContext {
 	t.Helper()
 	config := android.TestArchConfig(buildDir, nil)
-	config.ProductVariables.DeviceVndkVersion = StringPtr("current")
-	config.ProductVariables.Platform_vndk_version = StringPtr("VER")
+	config.TestProductVariables.DeviceVndkVersion = StringPtr("current")
+	config.TestProductVariables.Platform_vndk_version = StringPtr("VER")
 
 	return testCcWithConfig(t, bp, config)
 }
@@ -197,7 +197,7 @@
 func testCcNoVndk(t *testing.T, bp string) *android.TestContext {
 	t.Helper()
 	config := android.TestArchConfig(buildDir, nil)
-	config.ProductVariables.Platform_vndk_version = StringPtr("VER")
+	config.TestProductVariables.Platform_vndk_version = StringPtr("VER")
 
 	return testCcWithConfig(t, bp, config)
 }
@@ -205,8 +205,8 @@
 func testCcError(t *testing.T, pattern string, bp string) {
 	t.Helper()
 	config := android.TestArchConfig(buildDir, nil)
-	config.ProductVariables.DeviceVndkVersion = StringPtr("current")
-	config.ProductVariables.Platform_vndk_version = StringPtr("VER")
+	config.TestProductVariables.DeviceVndkVersion = StringPtr("current")
+	config.TestProductVariables.Platform_vndk_version = StringPtr("VER")
 
 	ctx := createTestContext(t, config, bp)