Add exception_wrapper::from_exception_ptr taking by &&

Summary: [Folly] Add `exception_wrapper::from_exception_ptr` taking by `&&`, permitting callers to move, since `std::exception_ptr` copy is expensive and `std::rethrow_exception` takes by value.

Reviewed By: ericniebler, markisaa

Differential Revision: D23016839

fbshipit-source-id: c07695fef0828a50426fe4e2b40fae9582c7ffd9

folly/ExceptionWrapper.cpp

@@ -63,11 +63,16 @@ std::exception const* get_std_exception_(std::exception_ptr eptr) noexcept {
 
 exception_wrapper exception_wrapper::from_exception_ptr(
     std::exception_ptr const& ptr) noexcept {
+  return from_exception_ptr(folly::copy(ptr));
+}
+
+exception_wrapper exception_wrapper::from_exception_ptr(
+    std::exception_ptr&& ptr) noexcept {
   if (!ptr) {
     return exception_wrapper();
   }
   try {
-    std::rethrow_exception(ptr);
+    std::rethrow_exception(std::move(ptr));
   } catch (std::exception& e) {
     return exception_wrapper(std::current_exception(), e);
   } catch (...) {

folly/ExceptionWrapper.h

@@ -379,6 +379,8 @@ class exception_wrapper final {
  public:
   static exception_wrapper from_exception_ptr(
       std::exception_ptr const& eptr) noexcept;
+  static exception_wrapper from_exception_ptr(
+      std::exception_ptr&& eptr) noexcept;
 
   //! Default-constructs an empty `exception_wrapper`
   //! \post `type() == none()`