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/algorithm b/include/algorithm
index 55e1f9f..1359fda 100644
--- a/include/algorithm
+++ b/include/algorithm
@@ -646,6 +646,7 @@
 #include <iterator>
 #include <cstddef>
 #include <bit>
+#include <version>
 
 #include <__debug>