noexcept applied to <future>.

llvm-svn: 160607
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: a4820bc4d576a41cde664999b334cf18caf9831e
diff --git a/src/future.cpp b/src/future.cpp
index 2935711..feb37e4 100644
--- a/src/future.cpp
+++ b/src/future.cpp
@@ -47,7 +47,7 @@
 }
 
 const error_category&
-future_category()
+future_category() _NOEXCEPT
 {
     static __future_error_category __f;
     return __f;