Build noelle with release version of LLVM and fix building different versions

[gchan510]

Current build time for NOELLE is very slow when using clang.
Possible solution: Build with release version of clang but still have ability to use debugging symbols from LLVM

Also, noelle is set up in a way such that if a build directory exists in the library that is being built, the library will be skipped.
This is not the behavior we want when we want to build a release and a debug version of noelle.
Solution: Run make clean inside noelle/src before building another version