[wasm] disable trap handlers by default in d8

Enabling trap handlers has been causing problems with sanitizers, stress bots,
clusterfuzz, etc. Some of these fixes will require more in depth changes. In the
meantime, this restores the original behavior so the bots can turn green again.

This change reverts https://crrev.com/c/673548.

Bug: v8:6924
Change-Id: I4277ae53bc98f9896b800d015fda2ce68ae9e6f5
Cq-Include-Trybots: master.tryserver.v8:v8_linux64_tsan_concurrent_marking_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/718480Reviewed-by: Mircea Trofin <mtrofin@chromium.org>
Commit-Queue: Eric Holk <eholk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48563}

src/d8.cc

@@ -2807,10 +2807,14 @@ bool Shell::SetOptions(int argc, char* argv[]) {
 
 // On x64 Linux we want to enable the Wasm trap handler by default. Setting
 // the flag here allows the command line argument to still override it.
-#if V8_OS_LINUX && V8_TARGET_ARCH_X64
+//
+// Currently we leave the default unchanged for sanitizers.
+//
+// TODO(eholk): enable trap handlers on sanitizers once issues are resolved.
+#if !defined(V8_USE_ADDRESS_SANITIZER) && !defined(LEAK_SANITIZER) && \
+    !defined(THREAD_SANITIZER) && V8_OS_LINUX && V8_TARGET_ARCH_X64
   SetFlagsFromString("--wasm-trap-handler");
 #endif
-
   v8::V8::SetFlagsFromCommandLine(&argc, argv, true);
 
   // Set up isolated source groups.