Several fixes

[rhabacker]

The commits from this pr fix problems discovered when building binary packages for the openSUSE distribution, build vsgvr on Linux and Windows MinGW.

They are tested on the Open SUSE build service for example mingw32-vsgvr, mingw64-vsgvr and vsgvr for linux.

They are also needed for further work on #15, since the tests will be based on the use of portable binary packages for Windows built from the above packages.

[rhabacker]

There is one remaining thing, using openXR from a distribution package.

[geefr]

I'm not sure things are ready to be added to package managers just yet, but all looks good in principle. There are a lot of changes here, some probably clash with changes I already have, or areas of code that are about to be refactored heavily.

But very much appreciated, will take me a while to integrate - (Ignoring my limited free time) I need to get through a bunch of vsg fixes, then some OpenXR / core features for vsgvr to be actually useful (for a 1.0 at some point). Short version is we're about 80% of the way towards a usable set of functionality, and there's possibly changes to move down to vsg itself at some point.

Some questions for now, otherwise I'll pull commits in when I can:

• Are you planning many more fixes / changes?
• Are the suse packages for a specific purpose / to be used by some downstream applications, or just general work to get things building?

[rhabacker]

Are you planning many more fixes / changes?

Most of the fixes were added to address build issues I encountered when building packages for Linux and Windows (cross-compiled). I do not currently plan to make any major changes to the feature set.

Since I'm not quite done with testing yet, there may still be some minor fixes needed.

[rhabacker]

I'm not sure if things are ready to be added to package managers yet,

I use these packages in a personal namespace to get mostly reproducible builds for testing and validation on different platforms and hosts. We are maintaining an osg based VR application and want to see to what extent we could switch to vsg on the supported platforms and what that is missing.

but in principle everything looks good.

Good to hear, I tried to separate the commits by topic.

There are a lot of changes here,

There are three topics:

1. cmake installation fixes including finding an installed OpenXR package.
   2583d89 Fix static and shared building on Windows
   0b39b86 Use cmake related install settings from vsg
   4fbd0cf Add support to find installed vsgvr data files
   3ab8a26 Add support to install binaries and files
   a3d8f68 Install versioned vsgvr library (packaging requirement)
   421cdc3 Add support to use OpenXR sdk from distribution
   07b51cb Fix finding include headers

2. toolchain related source code build fixes
   e4a3b77 Fix possible crash in OpenXRActionPoseBinding::destroyActionSpace()
   081f2a3 Fix build error with gcc 7.5: 'cerr|cout' is not a member of 'std'.
   6395742 Fix build error: cannot convert 'std::nullptr_t' to 'XrSpace' {aka 'long long unsigned int'} in assignment

3. other nice to have commits
   5285688 Cleanup displaying errors and exit code
   185e4cb Use additional cmake related macros from vsg
   0a0c103 Use vsg provided macro vsg_add_feature_summary()
   8c3ede1 Create and install executable as `vsgvrviewer' in order to use a consistent name

Topic 1. and 2. are needed to e.g. build a package on windows

some probably clash with changes I already have, or areas of the code that will be heavily refactored.

Which commits are you referring to?

[geefr]

(No need to worry about the conflicts I'm causing, I'll probably have a fair few more, then think about the cmake changes/etc)

[geefr]

@rhabacker Okay almost all of this was merged without issue. I'm reasonably confident it hasn't broken things too badly, but have only checked the windows build so far. I'll check Android shortly, Linux when I have time.

The CMake bits for cppcheck/clangformat/doxygen/clobber are turned off for now, they weren't working right with visual studio, and there's a lot to fix before thinking about code style :)

Thanks for the fixes - If anything's broken or there's other tweaks, best to raise an issue before the PR. Upcoming plans involve trying to use vsgvr for some more demos, which I'm sure will mean I need to go back and rewrite some things extensively..