Implement the infrastructure for feature-test macros. Very few actual feature test macros, though. Reviewed as: https://reviews.llvm.org/D51955

llvm-svn: 342073
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: f56972e22489c92028e5147344ab8b31b0b4fed5
diff --git a/include/numeric b/include/numeric
index 70ef173..4e68239 100644
--- a/include/numeric
+++ b/include/numeric
@@ -142,6 +142,7 @@
 #include <iterator>
 #include <limits> // for numeric_limits
 #include <functional>
+#include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header