`cmQtAutoGenerator` automatically started a libuv loop in the constructor.
The loop is needed in `cmQtAutoGeneratorMocUic`, but not in
`cmQtAutoGeneratorRcc` (anymore).  To avoid starting the loop in
`cmQtAutoGeneratorRcc`, this patch moves the loop variables and startup code
from `cmQtAutoGenerator` to `cmQtAutoGeneratorMocUic`.