Fixing up some ABI issues

llvm-svn: 134639
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 11af28bdbdff9132d225014ce4964b1bc56370cf
diff --git a/include/future b/include/future
index 48b84cf..9f3780b 100644
--- a/include/future
+++ b/include/future
@@ -452,6 +452,8 @@
 
     _LIBCPP_INLINE_VISIBILITY
     const error_code& code() const throw() {return __ec_;}
+
+    virtual ~future_error() _NOEXCEPT;
 };
 
 class __assoc_sub_state