fix folly/lang/ExceptionTest.cpp under libc++

Summary: Fix the uncaught-exception termination message expectations in `folly/lang/ExceptionTest.cpp` under libc++.

Reviewed By: markisaa

Differential Revision: D26328622

fbshipit-source-id: 2e2f9fce93c65556508d99d1f7b80f0971f35c0c

folly/lang/test/ExceptionTest.cpp

@@ -50,12 +50,12 @@ extern "C" FOLLY_KEEP void check_cond_folly_terminate_with(bool c) {
 template <typename Ex>
 static std::string message_for_terminate_with(std::string const& what) {
   auto const name = folly::pretty_name<Ex>();
-  auto const prefix =
-      std::string("terminate called after throwing an instance of ");
+  std::string const p0 = "terminate called after throwing an instance of";
+  std::string const p1 = "terminating with uncaught exception of type";
   // clang-format off
   return
-      folly::kIsGlibcxx ? prefix + "'" + name + "'\\s+what\\(\\):\\s+" + what :
-      folly::kIsLibcpp ? prefix + name + ": " + what :
+      folly::kIsGlibcxx ? p0 + " '" + name + "'\\s+what\\(\\):\\s+" + what :
+      folly::kIsLibcpp ? p1 + " " + name + ": " + what :
       "" /* empty regex matches anything */;
   // clang-format on
 }