libc-test: allow deprecated functions

glibc-2.24 deprecates readdir_r() and readdir64_r()
diff --git a/libc-test/build-generated.rs b/libc-test/build-generated.rs
index 41b5627..a51c0e3 100644
--- a/libc-test/build-generated.rs
+++ b/libc-test/build-generated.rs
@@ -10,6 +10,7 @@
         .flag("-Wall")
         .flag("-Wextra")
         .flag("-Werror")
+        .flag("-Wno-deprecated-declarations")
         .flag("-Wno-type-limits")
         .compile("liball.a");
 }