REG 1.42.0-beta1: Obj-C related compile error on Linux and misleading error location

[s-ludwig]

Receiving the following error on Linux that doesn't occur for 1.41.0:

app-desktop/source/krtek/desktop/gui/panes/metadata.d(618,55): Error: Runtime function `objc_opt_isKindOfClass` was not found
                            auto btn = cast(ListIconButton)tsi.extraWidgets[0];
                                                                           ^

The location associated with the error does not have anything to do with extern (Objective-C), but there are other parts of the code base that do call Objective-C functions, but obviously only when compiling for Apple platforms. AFAICS, all such code is in version (iOS) or version (OSX) blocks.

[LunaTheFoxgirl]

This issue is related to this
#5034

So it affects more than just TypeInfo.