Removed all of llvm-lit's dependence on DejaGNU. A few things
are now broken and will be fixed shortly.
* Do not ignore lit.local.cfg files needed for llvm-lit
* Ignore lit.site.cfg file.
Add lit.local.cfg file for test/Concrete so no tests are executed
in this directory. I don't know why these tests are here, they
weren't executed before by DejaGNU.
Fixed tests where llvm-gcc was called without the -emit-llvm flag.
DejaGNU testing used to have this flag in its substitution variable
but for llvm-lit this has not been done.

I could replicate what DejaGNU did but by forcing developers to be
explicit when creating LLVM bitcode

* Remove test suite inconsistentcies. Some tests explictly use
  -emit-llvm
* Allows for tests to be written in the future that invoke
  the compiler as a native compiler
Added Runtime/POSIX/lit.local.cfg file that prevents the POSIX
tests from being executed if not enabled at configure time.
Only run SELinux test if support for SELinux was detected at configure
time.