…pendency

hyphen's sources in tarbals are identical, and the version from
pkgs properly supports cross compilation.

This reverts commit 6e27bc9.

propagate less of them

…qmakeFlags

but don't use __structuredAttrs

Add to qtbase support for building a small bootstrap package.

Move qmake and other tools from qtbase.dev to qtbase.qmake
to avoid pulling in a second version of qtbase.dev in cross builds.

Use hidden bootstrap packages for qtbase and qttools instead of
overrideScope-based staging process to solve some spurious builds
and infinite recursions.

This commit by itself will allow to cross compile only qttranslations
and qtbase.

Also teach the setup hook, qmake and cmake scripts to search various
build tools in PATH and use them for cross compilation.

This will allow to cross compile packages that require only qtbase and
qmake.

… a native-built one

For this we need to dynamically detect cross compilation in qtbase-setup-hook.sh
and in mkspecs, and stop unconditionally using binary lndir in propagatedNativeBuildInputs.

For now qtbase substitution will work only in one (most used) direction, and in many cases
will additionally require to manually add a buildHost version of qtbase.qmake to
nativeBuildInputs of the package that depends on qtbase.

Without it qtwebchannel will fail to find some library includes,
qtquickcontrols will refuse to build without properly failing the
build:
```
Some of the required modules (qtHaveModule(quick)) are not available.
Skipped.
```
And there are probably more problems, not always obvious.

It needs only qtdeclarative to build, not qtquickcontrols.

If you're a nativeBuildInput somewhere, you probably shouldn't propagate
qtbase.

…s with qttools as a buildInput

And don't propagate qtbase to avoid pulling in a second qtbase.dev in
cross builds.

https://github.com/NixOS/nixpkgs/blob/master/doc/builders/special/makesetuphook.section.md

Not sure why it was done.

This reverts commit 49e8d9d.

I expect here that qtwebengine will propagate qtwebchannel and qtdeclarative and that
qtdeclarative will propagate itself as a nativeBuildInput. But maybe we
shouldn't rely on those propagations?