dnl @synopsis AC_CHECK_ENVVAR
dnl
dnl This macro tests if a particular environment variable is defined.
dnl Warning if not.
dnl
dnl Example:
dnl
dnl     AC_CHECK_ENVVAR(foo)
dnl

AC_DEFUN([AC_CHECK_ENVVAR],[dnl
AC_MSG_CHECKING([variable $1])
if test -z @S|@$1; then
	AC_MSG_RESULT([no])
	AC_MSG_WARN([environment variable $1 not defined])
else
	AC_MSG_RESULT([@S|@$1])
fi
])