Fix FreeBSD 15 CI

(backport <rust-lang#3797>)
(cherry picked from commit 147222d)

Author: devnexen

libc-test/build.rs

@@ -2311,6 +2311,12 @@ fn test_freebsd(target: &str) {
             // should've been used anywhere anyway.
             "TDF_UNUSED23" => true,
 
+            // Removed in FreeBSD 15
+            "TDF_CANSWAP" | "TDF_SWAPINREQ" => true,
+
+            // Unaccessible in FreeBSD 15
+            "TDI_SWAPPED" | "P_SWAPPINGOUT" | "P_SWAPPINGIN" => true,
+
             // Removed in FreeBSD 14 (git a6b55ee6be1)
             "IFF_KNOWSEPOCH" => true,