This can be used by KF5 libraries to generate python 2 and 3 bindings.

When sip is executed it is passed one .sip file.  However, it uses that
to generate multiple cpp source files, one per class in the sip file.

Buildsystems need to know the outputs of commands, so this does not work
well as the output can't easily be predicted.

So, create a unity build of all files to compile into the python module.

The ruleset is used to transform or omit artifacts in C++ header files
when determining the SIP content to generate.  Some content common to
all Qt-using libraries can be processed by using the rule set present
here.  For example, most Q_METATYPE internal declarations should be
discarded.

These files process C++ headers with libclang and python-clang bindings,
using the AST to generate SIP files for PyQt binding library generation.

The design allows for further extensions which can process other
artifacts found in headers.  This iteration of the design is a simple
minimum which suffices to generate headers for KItemModels and some
other libraries.

FindPoppler wasn't available in ecm < 5.19

CCMAIL:faure@kde.org

At least Okular and KBibTex include a FindPoppler.cmake module but this one
uses the new ECMFindModuleHelpers and has imported targets.

REVIEW: 126183

REVIEW: 126414

The XINPUT library is unlikely to be available on many systems,
including a lot of Linux distributions. This will warn developers in
advance by (a) not searching for XINPUT unless it was explicitly
requested, and (b) printing a warning if they do request it.

REVIEW: 125935

REVIEW: 123470