Fix cross-compiling ios targets with cmake 3.14 as #88 states (#93)

* Rename target variable to target_triple

* Remove a bit of code duplication

* Add GenericTarget with several override points

* Add support for cross-compiling Apple targets with cmake 3.14

* Removed lazy_static and regex

Co-authored-by: Kyle Fleming <kyle@kylefleming.net>

Author: simlay