Make MTE tests pass with all values of MEMTAG_OPTIONS.

Do not assume that tests start with Sync MTE; check the initial setting
and change test logic as appropriate.

Bug: 192480262
Test: bionic-unit-tests with MEMTAG_OPTIONS=(off|sync|async)
Change-Id: Id80301e6426af16f89bd80a7a7ab127b6fd60425
diff --git a/tests/mte_test.cpp b/tests/mte_test.cpp
index f329d8d..ade9532 100644
--- a/tests/mte_test.cpp
+++ b/tests/mte_test.cpp
@@ -38,7 +38,7 @@
 #endif
   }
 #if defined(__aarch64__)
-  if (mte_supported()) {
+  if (mte_supported() && running_with_mte()) {
     EXPECT_DEATH(
         {
           volatile int load ATTRIBUTE_UNUSED = *mistagged_p;