On UNIX (but not Darwin) the username needs to be respected when creating a
temporary module directory, so that different users don't pollute each others'
module caches.
llvm-svn: 251340
There are still a bunch of dependencies on the plug-in, but this helps to
identify them.
There are also a few more bits we need to move (and abstract, for example the
ClangPersistentVariables).
llvm-svn: 248612
Adrian McCarthy