Add test configuration for the switch interpreter.

Bug: 31358597
Test: ./art/test/testrunner/run_build_test_target.py art-interpreter-cxx
Change-Id: Iebb7a3a5168a27654984f3749a7b86542422671b
diff --git a/build/art.go b/build/art.go
index 0b5ee44..1c8be0f 100644
--- a/build/art.go
+++ b/build/art.go
@@ -53,6 +53,9 @@
 		cflags = append(cflags, "-DART_HEAP_POISONING=1")
 		asflags = append(asflags, "-DART_HEAP_POISONING=1")
 	}
+	if envTrue(ctx, "ART_USE_CXX_INTERPRETER") {
+		cflags = append(cflags, "-DART_USE_CXX_INTERPRETER=1")
+	}
 
 	if !envFalse(ctx, "ART_USE_READ_BARRIER") && ctx.AConfig().ArtUseReadBarrier() {
 		// Used to change the read barrier type. Valid values are BAKER, BROOKS,