use throw_exception in Arena

Summary: Use `throw_exception` consistently in `Arena` for consistency.

Differential Revision: D25637401

fbshipit-source-id: 92cda5acc09b871fed78044fa3f3fa2c41b01609

folly/memory/Arena-inl.h

@@ -34,7 +34,7 @@ void* Arena<Alloc>::allocateSlow(size_t size) {
   }
   if (sizeLimit_ != kNoSizeLimit &&
       allocSize > sizeLimit_ - totalAllocatedSize_) {
-    throw_exception(std::bad_alloc());
+    throw_exception<std::bad_alloc>();
   }
 
   if (size > minBlockSize()) {

folly/memory/Arena.h

@@ -74,8 +74,8 @@ class Arena {
         sizeLimit_(sizeLimit),
         maxAlign_(maxAlign) {
     if ((maxAlign_ & (maxAlign_ - 1)) || maxAlign_ > alignof(Block)) {
-      throw_exception(std::invalid_argument(
-          folly::to<std::string>("Invalid maxAlign: ", maxAlign_)));
+      throw_exception<std::invalid_argument>(
+          folly::to<std::string>("Invalid maxAlign: ", maxAlign_));
     }
   }