don't destory defaultElfCache in exit handlers

Summary:
As it might be used during global destruction (for example, to
symbolize unhandled exception happened at that time).

Reviewed By: luciang, ot

Differential Revision: D3238303

fb-gh-sync-id: 39d8a6f99d95e700586349436e961f3624c95718
fbshipit-source-id: 39d8a6f99d95e700586349436e961f3624c95718

folly/experimental/symbolizer/Symbolizer.cpp

@@ -171,8 +171,8 @@ bool parseProcMapsLine(StringPiece line,
 
 ElfCache* defaultElfCache() {
   static constexpr size_t defaultCapacity = 500;
-  static ElfCache cache(defaultCapacity);
-  return &cache;
+  static auto cache = new ElfCache(defaultCapacity);
+  return cache;
 }
 
 }  // namespace