[NaCl SDK] nacl_io: handle null irt function pointers

native_client_sdk/src/libraries/nacl_io/kernel_wrap_newlib.cc

Index: native_client_sdk/src/libraries/nacl_io/kernel_wrap_newlib.cc
diff --git a/native_client_sdk/src/libraries/nacl_io/kernel_wrap_newlib.cc b/native_client_sdk/src/libraries/nacl_io/kernel_wrap_newlib.cc
index ebe8dd528bb1d3d61ace938baaed2fe2b291611e..833ed05a08c210e0ea399550735a25c849572a70 100644
--- a/native_client_sdk/src/libraries/nacl_io/kernel_wrap_newlib.cc
+++ b/native_client_sdk/src/libraries/nacl_io/kernel_wrap_newlib.cc
@@ -316,7 +316,7 @@ int _real_lseek(int fd, off_t offset, int whence, off_t* new_offset) {
 }
 
 int _real_mkdir(const char* pathname, mode_t mode) {
-  CHECK_REAL(mkdir);
+  CHECK_REAL_NOSYS(mkdir);
   return REAL(mkdir)(pathname, mode);
 }
 
@@ -336,7 +336,7 @@ int _real_munmap(void* addr, size_t length) {
 }
 
 int _real_open(const char* pathname, int oflag, mode_t mode, int* newfd) {
-  CHECK_REAL(open);
+  CHECK_REAL_NOSYS(open);
   return REAL(open)(pathname, oflag, mode, newfd);
 }
 
@@ -350,7 +350,7 @@ int _real_read(int fd, void* buf, size_t count, size_t* nread) {
 }
 
 int _real_rmdir(const char* pathname) {
-  CHECK_REAL(rmdir);
+  CHECK_REAL_NOSYS(rmdir);
   return REAL(rmdir)(pathname);
 }