[libc++] Add the version header to all headers.

Some headers which require the version header depend on other headers to
provide it. Include the version header in all top-level headers to make
sure a header cleanup can't remove the version header.

Note this doesn't add the version header to the c headers.

Reviewed By: #libc, Quuxplusone, ldionne

Differential Revision: https://reviews.llvm.org/D116172

NOKEYCHECK=True
GitOrigin-RevId: bd6e6846e7f431e9d84b1f257d4a0c8ddeac4fe2
diff --git a/include/fstream b/include/fstream
index 3d64adc..fc0a920 100644
--- a/include/fstream
+++ b/include/fstream
@@ -187,6 +187,7 @@
 #include <cstdlib>
 #include <istream>
 #include <ostream>
+#include <version>
 
 #if !defined(_LIBCPP_HAS_NO_FILESYSTEM_LIBRARY)
 #   include <filesystem>