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/exception b/include/exception
index b517486..7fd9279 100644
--- a/include/exception
+++ b/include/exception
@@ -81,6 +81,7 @@
 #include <cstddef>
 #include <cstdlib>
 #include <type_traits>
+#include <version>
 
 #if defined(_LIBCPP_ABI_MICROSOFT) && !defined(_LIBCPP_NO_VCRUNTIME)
 #include <vcruntime_exception.h>