libroot: Fix open flags in shm_open.

We need O_CLOEXEC here, not FD_CLOEXEC (which is equal to 0x1, which
in openflags is O_WRONLY and thus leads to the conflicts caught by
the previous commit.)

Fixes haikuports/haikuports#7524.

src/system/libroot/posix/sys/mman.cpp

@@ -216,7 +216,7 @@ shm_open(const char* name, int openMode, mode_t permissions)
 	if (error != B_OK)
 		RETURN_AND_SET_ERRNO(error);
 
-	return open(path, openMode | FD_CLOEXEC, permissions);
+	return open(path, openMode | O_CLOEXEC, permissions);
 }