[NaCl SDK] nacl_io: handle null irt function pointers

native_client_sdk/src/libraries/nacl_io/kernel_wrap_glibc.cc

Index: native_client_sdk/src/libraries/nacl_io/kernel_wrap_glibc.cc
diff --git a/native_client_sdk/src/libraries/nacl_io/kernel_wrap_glibc.cc b/native_client_sdk/src/libraries/nacl_io/kernel_wrap_glibc.cc
index a264eebd71796437b8cf1800086d0d5e8e1ba609..587482018913b4dc050f3820835a97c5e727ecd4 100644
--- a/native_client_sdk/src/libraries/nacl_io/kernel_wrap_glibc.cc
+++ b/native_client_sdk/src/libraries/nacl_io/kernel_wrap_glibc.cc
@@ -594,7 +594,7 @@ 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);
 }
 
@@ -614,12 +614,12 @@ 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);
 }
 
 int _real_open_resource(const char* file, int* fd) {
-  CHECK_REAL(open_resource);
+  CHECK_REAL_NOSYS(open_resource);
   return REAL(open_resource)(file, fd);
 }
 
@@ -629,7 +629,7 @@ 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);
 }