provide ~future_error() definition

llvm-svn: 134663
diff --git a/libcxx/src/future.cpp b/libcxx/src/future.cpp
index 98c7805..4c3a3fa 100644
--- a/libcxx/src/future.cpp
+++ b/libcxx/src/future.cpp
@@ -59,6 +59,10 @@
 {
 }
 
+future_error::~future_error() _NOEXCEPT
+{
+}
+
 void
 __assoc_sub_state::__on_zero_shared() _NOEXCEPT
 {