Description of Problem:

As per the "edb7212/configtool bug in 1.5.7" thread on the internal
ecc-config list on 2001-12-05, libcdl and the build tools need to allow
some public replacement for the internal ecos.db targets that use
enable/disable/set_value.

Here's Bart's intended solution:
    >> Now, any enable/disable/set_value entries in the ecos.db file for
that
    >> target would be turned into "requires" constraints associated with
    >> this configuration option. So if the user selects a target
    >> edb7212 then there would now a constraint in the system
    >> 'requires { CYGHWR_HAL_ARM_EDB7XXX_VARIANT == "EP7212"}'.
    >> It would now be up to the inference engine to modify
    >> CYGHWR_HAL_ARM_EDB7XXX_VARIANT accordingly, and users cannot mess
    >> things up without getting reports of conflicts. Also, other CDL
could
    >> start using CYGHWR_TARGET for e.g. determining default values.