[Development] New configuration system docs and FBX issues

[Sean Harmer]

Hi,

is there any documentation for the new configuration system please?

My specific issue is that I need a config test that uses different 
library names on each platform and I can't see how to achieve this. On 
windows I want the FBX config test in Qt 3D to link against the static 
FBX library libfbxsdk-md.lib whereas on linux it would be 
libfbxsdk-static.a and on macOS libfbxsdk.a.

An additional complication is that if we're building in debug and 
release build, the FBX SDK has the libs for these in different 
directories so we can't just rely upon passing the full -L 
path/to/fbxsdk/lib/platform/arch/{debug|release} to configure as if we 
pass debug we can't find the release lib and vice versa.

If we can solve this then hopefully we can build the FBX plugin as part 
of the official build and not have to rely upon users to build it 
themselves.

Thanks in advance for any help/pointers.

Sean