config.mk: All options in DEFAULTS are now defined in opt_global.h

[imp]

Summary

To simplify management of all the options that should be enabled for the
different architectures, adopt the convention that all options listed in
DEFAULTS will be #defined to 1 in opt_global.h for untied builds. Except
for GEOM_* and ISAPNP, they are all in opt_global.h. ISAPNP is a
opt_dontuse.h, so only filter GEOM_*.

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