LibC: Stub mlock in sys/mman

mlock is supposed to prevent memory from being paged out to swap, which
we don't have currently.

Required by OpenSSL.

Userland/Libraries/LibC/sys/mman.cpp

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/Format.h>
 #include <errno.h>
 #include <stdio.h>
 #include <string.h>
@@ -82,4 +83,10 @@ void* allocate_tls(const char* initial_data, size_t size)
     }
     return (void*)rc;
 }
+
+int mlock(const void*, size_t)
+{
+    dbgln("FIXME: Implement mlock()");
+    return 0;
+}
 }