[libc++] Properly guard flat_map includes based on C++ version

[ldionne]

That's what we (try to) do consistently for all other umbrella headers.

As a drive-by, remove the <__assert> header which is not mandated anymore.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Louis Dionne (ldionne)

Changes

That's what we (try to) do consistently for all other umbrella headers.

---

Full diff: https://github.com/llvm/llvm-project/pull/119227.diff

1 Files Affected:

• (modified) libcxx/include/flat_map (+7-2)

diff --git a/libcxx/include/flat_map b/libcxx/include/flat_map
index 15d79dd1ddca34..870dd2e26a2379 100644
--- a/libcxx/include/flat_map
+++ b/libcxx/include/flat_map
@@ -39,8 +39,13 @@ namespace std {
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
-#include <__flat_map/flat_map.h>
-#include <__flat_map/sorted_unique.h>
+
+#if _LIBCPP_STD_VER >= 23
+#  include <__flat_map/flat_map.h>
+#  include <__flat_map/sorted_unique.h>
+#endif
+
+// for feature-test macros
 #include <version>
 
 // standard required includes