Better support build on *NIX platforms

[orzel7]

I'm trying to using library on Linux. This is very basic support, but in the future i am going to implement advanced things.

[ghost]

All CLA requirements met.

[bghgary]

Sorry @orzel7. We missed this PR somehow. I think it would be great if we can get some CI for linux before merging or this will break again.

[joaquin4d]

this PR is great, any timeframe for getting this merged?

[bghgary]

We can merge, but with a CI being added, it may break easily. Anyone want to take a stab at adding Linux CI?

[joaquin4d]

Don't see any docs explaining what you mean, so I ask. Do you mean:

• adding tests for linux? (but seems to me tests described in CMakeLists.txt don't exclude Linux platform)
• adding github actions for Linux? (but currently there are none anyway for any platform)
• adding a test specifically for testing if it builds on Linux? (but shouldn't this be just the act of compiling it on Linux?)

[bghgary]

We use Azure DevOps to do CI. It should be mostly just changing this file: https://github.com/microsoft/glTF-SDK/blob/master/Build/AzureDevOps/azure-pipelines.yml