nshlib/nsh_envcmds.c:  Fix warning g_oldpwd defined but not used [-Wunused-const-variable]
#if CONFIG_NFILE_DESCRIPTORS > 0 && !defined(CONFIG_DISABLE_ENVIRON)
static const char g_pwd[] = "PWD";
+#ifndef CONFIG_NSH_DISABLE_CD
static const char g_oldpwd[] = "OLDPWD";
+#endif
static const char g_home[] = CONFIG_LIB_HOMEDIR;
#endif
