Provide mprotect syscall

sysdeps/nacl/nacl_syscalls.h

Index: sysdeps/nacl/nacl_syscalls.h
diff --git a/sysdeps/nacl/nacl_syscalls.h b/sysdeps/nacl/nacl_syscalls.h
index d754849ca28d7cd42ce653b2884a109225284898..d25fa9ac242fb137073967e5f7bddb2c64d12a40 100644
--- a/sysdeps/nacl/nacl_syscalls.h
+++ b/sysdeps/nacl/nacl_syscalls.h
@@ -50,6 +50,8 @@
 
 #define NACL_sys_getdents               23
 
+#define NACL_sys_mprotect               24
+
 #define NACL_sys_exit                   30
 #define NACL_sys_getpid                 31
 #define NACL_sys_sched_yield            32
@@ -144,6 +146,8 @@ typedef void *(*TYPE_nacl_mmap) (void *start, size_t length,
 
 typedef int (*TYPE_nacl_munmap) (void *start, size_t length);
 
+typedef int (*TYPE_nacl_mprotect) (void *addr, size_t length, int prot);
+
 typedef void (*TYPE_nacl_thread_exit) (int32_t *stack_flag);
 typedef int (*TYPE_nacl_thread_create) (void *start_user_address,
                                         void *stack,