tree b37d0c2765ac3af01f7e10d44d944f7b494d051b
parent 44d158805cf0570211f26fa7af6e5a7a580a8ef8
author Ben Clayton <headlessclayton@gmail.com> 1574079741 +0000
committer Ben Clayton <bclayton@google.com> 1574082026 +0000

CMakeLists.txt: Make it easier to specify third_party vars.

Only set the third_party directory variables if they're not already set
(by the dependee project).