Running ./Setup.sh runs into problems with clang-3.9, as it believes clang-3.9 does not exist. After a few workarounds, I ended up hitting another wall :
MyUser.Username@thisPC ~/UnrealEngine $ ./Setup.sh
Registering git hooks... (this will override existing ones!)
dpkg-query: no packages found matching clang-3.9
Attempting installation of missing package: clang-3.9
+ sudo apt-get install -y clang-3.9
Reading package lists... Done
Building dependency tree
Reading state information... Done
Note, selecting 'python-clang-3.9' for regex 'clang-3.9'
You might want to run 'apt-get -f install' to correct these:
The following packages have unmet dependencies:
libdrm-dev : Depends: libdrm2 (= 2.4.70-1~ubuntu16.04.1) but 2.4.75+git1702140630.f6499b~gd~x is to be installed
E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).
I forgot to specify, I got it up and running after all of these problems, but my question is: What caused this clang-3.9 missing?