sys/mman.h: add MADV_WIPEONFORK from linux v4.14

allows zeroing anonymous private pages inherited by a child process.
new in linux commit d2cd9ede6e193dd7d88b6d27399e96229a551b19

include/sys/mman.h

@@ -72,6 +72,8 @@ extern "C" {
 #define MADV_NOHUGEPAGE  15
 #define MADV_DONTDUMP    16
 #define MADV_DODUMP      17
+#define MADV_WIPEONFORK  18
+#define MADV_KEEPONFORK  19
 #define MADV_HWPOISON    100
 #define MADV_SOFT_OFFLINE 101
 #endif