Qt4Macros: Remove unneeded generate CONDITION.
Qt4Macros: Remove undefined varible use.

This may have been added in anticipation of processing COMPILE_OPTIONS,
but as moc does not accept them, there is no need for it.
Qt4Macros: Simplify some variable population.
Docs: Document existing target property debugging options.
Docs: Trim trailing whitespace in generated doc.
Docs: Generalize and de-duplicate VISIBILITY_PREFIX docs.
Docs: Document variables for default visibility values.
Merge topic 'minor-cleanups' into next

79a7a81 Docs: Document variables for default visibility values.
6f6391b Docs: Generalize and de-duplicate VISIBILITY_PREFIX docs.
d8cb47f Docs: Trim trailing whitespace in generated doc.
f10e648 Docs: Document existing target property debugging options.
4f4d69f Qt4Macros: Simplify some variable population.
a413a40 Qt4Macros: Remove undefined varible use.
b60a29e Qt4Macros: Remove unneeded generate CONDITION.