Fix multiarch compatibility

[ghisvail]

At the moment, glbinding is not compatible with multiarch systems. This PR modifies the installation path variables and target settings to achieve this.

The first commit uses GNUInstallDirs to provide the multiarch install paths. This is a pretty standard solution and keeps the old behavior in case the system is not multiarch.

The second commit addresses CMake detection on multiarch (and non-multiarch) systems. The old settings were not flexible enough and not exactly compliant with what CMake recommends in their tutotrials. Considering the simplicity of your project (one library), the simplest solution is to put the CMake package config file alongside the target file and just include it.

Let me know whether you have any questions.

[scheibel]

Thanks for this PR.
Most of it looks promising but I'm not sure how the adapted cmake configure script handles multiple architectures and build-types (the first is your, the latter our requirement).

I will discuss this with the other maintainers.

[scheibel]

It may be that the differing build-types are actually another issue (cginternals/cmake-init#36).

[ghisvail]

It may be that the differing build-types are actually another issue (cginternals/cmake-init#36).

Indeed.

how the adapted cmake configure script handles multiple architectures

/usr/lib/cmake/<arch>/<project> is part of the default paths searched by CMake for config files, so is /usr/lib/cmake/<project> or usr/share/cmake/<project>. In Debian, the latter 2 are used for arch-independent libraries such as those which are headers-only.

...and build-types

CMake should create both a <target> and a <target>-<build_type> file in the CMake config path. You can have as many <target>-<build_type> as your number of supported build types (for instance Debug and Release). Then, find_package will do its magic and you can use generator expressions on the imported target to dispatch what is specific to Debug and Release respectively.

[n3rdopolis]

This commit seems to work pretty good, is there a reason why it was never merged?

[n3rdopolis]

@scheibel The changes in this PR still seems to work BTW.