[libc++] Granularize <concept> includes

Reviewed By: ldionne, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D137283
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
index 9b21e7b..e278722 100644
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -1917,6 +1917,7 @@
 
 #if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
 #  include <atomic>
+#  include <concepts>
 #  include <iterator>
 #  include <memory>
 #  include <stdexcept>