Increase exception stack trace length, because short traces are getting annoying.

c++/src/kj/exception.c++

@@ -85,7 +85,7 @@ String stringifyStackTrace(ArrayPtr<void* const> trace) {
   }
   KJ_DEFER(if (oldPreload != nullptr) { setenv("LD_PRELOAD", oldPreload.cStr(), true); });
 
-  String lines[8];
+  String lines[32];
   FILE* p = nullptr;
 
 #if __linux__

c++/src/kj/exception.h

@@ -114,7 +114,7 @@ private:
   Type type;
   String description;
   Maybe<Own<Context>> context;
-  void* trace[16];
+  void* trace[32];
   uint traceCount;
 
   friend class ExceptionImpl;