Workaround a bug resolving decltype'd locals in lambdas

Summary:
Then it's time to get food.
The bug report linked in the comment has more details.

Reviewed By: yfeldblum

Differential Revision: D4209389

fbshipit-source-id: 87e72691555992bdf964b0ded1173daadcedffa4

folly/futures/test/InterruptTest.cpp

@@ -22,12 +22,12 @@
 using namespace folly;
 
 TEST(Interrupt, raise) {
-  std::runtime_error eggs("eggs");
+  using eggs_t = std::runtime_error;
   Promise<Unit> p;
   p.setInterruptHandler([&](const exception_wrapper& e) {
-    EXPECT_THROW(e.throwException(), decltype(eggs));
+    EXPECT_THROW(e.throwException(), eggs_t);
   });
-  p.getFuture().raise(eggs);
+  p.getFuture().raise(eggs_t("eggs"));
 }
 
 TEST(Interrupt, cancel) {