* machinery for nonfatal warnings.
* new backend config-file keywords:
defparam -- like defopt, but each defparam option is required
to have a value when configured via "options".
defflag -- like defopt, but defflag options may not have a value.
Also, on "option FOO", a needs-count style flag
(NFOO, either 0 or 1) is emitted to the .h file.
* Warn about old-style options that aren't defined via def{opt,param,flag}
and which are added to IDENT. (These behave subtly differently
to defopt options when no explicit value is given.)
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