MAKE_LEVEL_ENV
Global_Set_ReadOnly(".MAKE.LEVEL.ENV", MAKE_LEVEL_ENV);
const char *ep = getenv(MAKE_LEVEL_ENV);
#ifndef MAKE_LEVEL_ENV
setenv(MAKE_LEVEL_ENV, level_buf, 1);
level = getenv(MAKE_LEVEL_ENV); /* we should preserve this */
setenv(MAKE_LEVEL_ENV, level, 1);