Add support for linking against static builds in CMake

This change reinstates functionality that was removed in
commit 102e1822ffcdc9954d3c698f863734a8083e349c. However, it
differs from the original implementation in several ways:

* It uses the QMAKE_PRL_LIBS variable, replacing whitespace with
  semicolons, rather than using a dedicated QMAKE_PRL_LIBS_FOR_CMAKE
  variable.
* More importantly, it parses the -L and -l flags and uses CMake's
  find_library() command to look for the libraries in the specified
  search paths, and then converts them to absolute paths. This is the
  same approach that CMake's own FindPkgConfig module uses to find
  libraries specified in this form. Any other flags not of the form
  -L or -l (for instance, -s flags passed to Emscripten) are added to
  the new INTERFACE_LINK_OPTIONS target property if the CMake version
  is 3.13 or newer.

The original implementation of this functionality was removed because
of the lack of absolute library paths. At the time, it was believed
that qmake would have to be modified to do its own equivalent of
find_library() to get the absolute paths to the libraries. However,
the approach taken by FindPkgConfig has proven robust enough to be
used here, allowing CMake to find the absolute paths to the libraries
without having to modify qmake.

[ChangeLog][CMake] Added support for automatic linking of transitive
dependencies in static builds

Fixes: QTBUG-38913
Change-Id: I7d9cdb0d339c6ef697b04099d129481c770fc0fc
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

0 files changed, 0 insertions, 0 deletions