ART: Disable check under memory tools

Disable a stack check under memory tools. It assumes a single
common stack, which seems violated at least under valgrind on
ARM.

Change-Id: Ida05adb0728cc46f3bbda4d34be7a1623bb3bc82
diff --git a/runtime/thread.cc b/runtime/thread.cc
index f1f4a12..748dfa5 100644
--- a/runtime/thread.cc
+++ b/runtime/thread.cc
@@ -940,7 +940,10 @@
   }
 
   // Sanity check.
-  CHECK_GT(FindStackTop(), reinterpret_cast<void*>(tlsPtr_.stack_end));
+  if (RUNNING_ON_MEMORY_TOOL == 0) {
+    // Sanitizers may be using a split stack. Ignore the check.
+    CHECK_GT(FindStackTop(), reinterpret_cast<void*>(tlsPtr_.stack_end));
+  }
 
   return true;
 }