OptimizeOnFirstUsageOption is ignored by compiler

This option is deprecated on Qt since 5.12. Konsole cmake minimal Qt version set is 5.12, giving warning messages while making.
A regular expression is automatically optimized the first time it is used now.

warning: ‘QRegularExpression::OptimizeOnFirstUsageOption’ is deprecated: This option does not have any effect since Qt 5.12 [-Wdeprecated-declarations]