selftests: add define for F_SEAL_FUTURE_WRITE

This is not defined in some cases leading to the memfd test
not compiling. Define it in the source file.

Orabug: 33891077

Signed-off-by: Larry Bassel <[email protected]>
Reviewed-by: John Donnelly  <[email protected]>

Author: Larry Bassel

tools/testing/selftests/memfd/memfd_test.c

@@ -943,6 +943,11 @@ static void test_seal_write(void)
  * Test SEAL_FUTURE_WRITE
  * Test whether SEAL_FUTURE_WRITE actually prevents modifications.
  */
+
+#ifndef F_SEAL_FUTURE_WRITE
+#define F_SEAL_FUTURE_WRITE     0x0010  /* prevent future writes while mapped */
+#endif
+
 static void test_seal_future_write(void)
 {
 	int fd, fd2;