Fix out-of-tree building

[DaveRichmond]

Pull request for the patch provided in issue #30. In tree building still appears to work fine with this change, so I can only assume it doesn't have any side effects.

• [x] I have thoroughly tested my contribution.
• [x] The code I submitted has no copyright issues.

Out of tree project building failed because the third_party libraries within the sdk weren't included in the sdks cmake files.

[GongT]

"add_subdirectory(third_party)" should be in CMakeLists.example.txt (and already in CMakeLists.txt)

I think your issue is about miss-synchronize between CMakeLists.example.txt and CMakeLists.txt.

[GongT]

Ok, I found it's ok to write this here, reopen this, please wait for review.

[cmdrf]

I had the same issue. It would be cool to merge this (after fixing indentation).