Mark a couple of move assignment operators as noexcept

Summary: MSVC informed me that these classes had noexcept move constructors but the move assignment operators were not marked as noexecpt.

Reviewed By: yfeldblum

Differential Revision: D19796949

fbshipit-source-id: d2bdc8ebb6d77709e367a4137fb0817c8006084f

folly/Benchmark.h

@@ -122,7 +122,7 @@ struct BenchmarkSuspender {
   }
 
   BenchmarkSuspender& operator=(const BenchmarkSuspender&) = delete;
-  BenchmarkSuspender& operator=(BenchmarkSuspender&& rhs) {
+  BenchmarkSuspender& operator=(BenchmarkSuspender&& rhs) noexcept {
     if (start != TimePoint{}) {
       tally();
     }

folly/detail/ThreadLocalDetail.h

@@ -317,7 +317,7 @@ struct StaticMetaBase {
       other.value = kEntryIDInvalid;
     }
 
-    EntryID& operator=(EntryID&& other) {
+    EntryID& operator=(EntryID&& other) noexcept {
       assert(this != &other);
       value = other.value.load();
       other.value = kEntryIDInvalid;