Disable DumpNativeStack.

Causes crashes on 004-ThreadStress, already was a no-op on the target.
Bug: 15446488

Change-Id: I9a1541b894087337dafa3fdde00d845f3542b141
diff --git a/runtime/utils.cc b/runtime/utils.cc
index f2d710d..9a4c875 100644
--- a/runtime/utils.cc
+++ b/runtime/utils.cc
@@ -1120,7 +1120,8 @@
 
 void DumpNativeStack(std::ostream& os, pid_t tid, const char* prefix,
     mirror::ArtMethod* current_method) {
-#ifdef __linux__
+  // TODO: enable on __linux__ b/15446488.
+#if 0
   // b/18119146
   if (RUNNING_ON_VALGRIND != 0) {
     return;