Relax the stack trace limit for opt mode too.

Summary:
Similar to D24179337 (https://github.com/facebook/folly/commit/7cc28784d1749283b7eb78399a0f0a77594dbc14).

Though I'm not actually sure what's causing the increase... maybe the right thing to do is the debug the underlying cause, but I'm also not sure how to debug this exactly.

Reviewed By: yfeldblum

Differential Revision: D24353676

fbshipit-source-id: 12bc5eae939f95d8d091280dc5b5af638f0152a0

folly/experimental/symbolizer/test/StackTraceSizeLimitTest.cpp

@@ -88,11 +88,11 @@ TEST(StackTraceSizeLimitTest, FiberLimit) {
   } else {
     if (folly::kIsSanitizeThread) {
       t(fBaseline, 2500);
-      t(fStack, 6800);
+      t(fStack, 9000);
       t(fHeap, 3500);
     } else {
       t(fBaseline, 1600);
-      t(fStack, 6800);
+      t(fStack, 9000);
       t(fHeap, 2200);
     }
   }