Externalize entry points that are marked internal

[keram88]

This adds a utility extern-statics that transforms input LLVM files to have functions which are entry-points to always be externally linkable. SMACK's front-end is changed to process input bit-codes before running llvm-link on them in order to keep these functions from being erased during linking.

The usage of extern-statics is:

• -in
• -out
• -entry-points <list,of,procedures>