[Development] Qt 6 buildsystem support requirements

[Edward Welbourne]

Singling out just one tiny corner of all that for a passing remark:

Jason Newton (1 August 2018 10:24)
> One of the things I like about the way bazel keeps this is I can jump
> back and forth between an optimized build and a full debug build (for
> example) - they don't erase eachother

This is easy to do in any build system that supports out-of-source
(a.k.a. "shadow") builds - notably including the existing qmake-based
builds for Qt.  I never want to do an in-source build of anything.

> and you can only achieve that jumping capability, being cheap, if you
> add a file-level layer of indirection.

Not sure what you're claiming here, or what system you're claiming lacks
it.  If you've got both optimised and debug builds, you're going to have
both sets of files *somewhere* (whether jumbled up in one directory or
kept separate in two out-of-source build trees).

	Eddy.