I initially hit this too (running Xcode 8.2.1). However the errors were resolved by running "xcode-select --install" in a terminal session. It seems that the latest Xcode releases don't install the command-line tools by default, which is what the xcode-select command does when run, and they are presumably required for some parts of the build.
After doing that, Tunnelblick built successfully for me, and appears to work fine.
Having said that, I am now trying to follow the rebranding process, and am hitting issues there... After following the steps and attempting a build, it appears to get most of the way through before failing and telling me "An Xcode preference must be set to put build products in the 'tunnelblick/build' folder. Pleas set Xcode preference > Locations > Advanced to 'Legacy'". However I've already done that (and I double-checked, and it is still set to "Legacy"). Considering a non-rebranded build succeeded, I assume I'm missing a step in the rebranding process somewhere.
Alex