Update Qt5 ports to 5.9.3.

This took quite a lot of time because Qt's own build system underwent
several changes in 5.8.0 that took a while to adapt to.

And, of course, qt5-webengine is a behemoth that we need to patch like crazy
due to its bundling of Chromium. In fact, most of the Chromium patches in
qt5-webengine have been imported with no changes from www/chromium@433510
("www/chromium: update to 56.0.2924.87").

New port: accessibility/qt5-speech

Bigger changes to Qt5 ports we had to make:

• Qt now allows using a configure.json file to define configuration options and specify configuration checks that can be done when qmake is invoked. However, configure.json checks done in a subdirectory only propagates to subdirectories, and checks elsewhere will fail if all .pro files are being parsed at once (i.e. qmake -recursive), so several ports had to switch to USES=qmake:norecursive along with manual additional qmake invocations in subdirectories in order to work. It's been mentioned in a few places such as Qt's bug tracker that qmake's recursive mode is pretty much deprecated, so we might switch to non-recursive mode by default in the future.

• Uses/qmake.mk: Introduce QMAKE_CONFIGURE_ARGS. qmake now accepts arbitrary options such as '-foo' and '-no-bar' at the end of the command-line. They can be specified in QMAKE_CONFIGURE_ARGS.

• graphics/qt5-wayland: The port can only be built if graphics/mesa-libs is built with the WAYLAND option, so a corresponding option (off by default) was added to the port.

• misc/qt5-doc: Switch to a pre-built documentation tarball. The existing port was not working with Qt 5.9. Instead of trying to fix it, switch to what Gentoo does and fetch a tarball that already contains all documentation so that we do not have to build anything at all. The tarball's name and location in download.qt.io look a bit weird, but it seems to work fine.

• www/qt5-webengine: Use binutils from ports, Chromium's GN build system generates a build.ninja that uses ar(1) with the @file syntax that is not supported by BSD ar, so we need to use GNU ar from binutils.

• x11-toolkits/qt5-declarative-render2d: This port was merged into the main Qt Declarative repository upstream, and into x11-toolkits/qt5-quick in the ports tree.

Changes to other ports we had to make:

• biology/ugene: Drop a '#define point "."' that is not present in more recent versions of the port. Defining a macro with such a common name causes build issues with Qt 5.9, which uses |point| as an argument name in methods.

• cad/qelectrotech: Fix plist with Qt 5.9. Directories are no longer installed with cp -f -R', but rather qmake install qinstall', which does not install
  
  %%DATADIR%%/elements/10_electric/20_manufacturers_articles/bosch_rexroth/.directory
  
  That's a local file that should not even have been part of the tarball anyway.

• chinese/gcin-qt5: Add additional private Qt directories (which should not be used in the first place) to get the port to build with Qt 5.9.

• devel/qtcreator: Fix plist with Qt 5.9. Something changed in qdoc and some test classes no longer generate documentation files.

• security/keepassx-devel: Import a patch sent upstream almost a year ago to fix the build with Qt 5.9.

Thanks to antoine for the exp-run, and tcberner and Laurent Cimon
<laurent@nuxi.ca> for landing changes in our qt-5.9 branch.

PR: 224849