Fix global statics

Summary:
Statics in headers are bad.

Test Plan: run unit tests

Reviewed By: robbert@fb.com

Subscribers: trunkagent, sdwilsh, njormrod, folly-diffs@

FB internal diff: D1646906

Tasks: 5486739

Signature: t1:1646906:1415042805:dc4d1cec54e9320f1e609808a73622c731a4cdc9

folly/DynamicConverter.h

@@ -168,7 +168,7 @@ public:
 
 // conversion factory
 template <typename T, typename It>
-static inline std::move_iterator<Transformer<T, It>>
+inline std::move_iterator<Transformer<T, It>>
 conversionIterator(const It& it) {
   return std::make_move_iterator(Transformer<T, It>(it));
 }

folly/test/SynchronizedTestLib-inl.h

@@ -30,14 +30,16 @@
 #include <folly/Synchronized.h>
 
 
-static const auto seed = folly::randomNumberSeed();
-typedef std::mt19937 RandomT;
-static RandomT rng(seed);
+inline std::mt19937& getRNG() {
+  static const auto seed = folly::randomNumberSeed();
+  static std::mt19937 rng(seed);
+  return rng;
+}
 
 template <class Integral1, class Integral2>
 Integral2 random(Integral1 low, Integral2 up) {
   std::uniform_int_distribution<> range(low, up);
-  return range(rng);
+  return range(getRNG());
 }
 
 template <class Mutex>