Implemented cleanups as suggested by Chris:

* Use Module::getNamedFunction() to delete "main" instead of using a loop
* Compare function pointers instead of function names to determine equivalence
* Simplified creation of a 2-element vector containing zeroes
* Manually performed LICM on code
* Added an abort() in case a function we're considering occurs in something that
  is not an instruction
* Use DEBUG() around code sections instead of just in a statement in a loop,
  because GCC's DCE may not be good enough to completely remove it in a release
  build
* Print out a command that can be directly copied-and-pasted to re-execute
* Instead of just checking if a symbol begins with a dot and fixing it
  accordingly, use Mangler and fix all the problems (invalid chars in C symbol
  names) entirely
* The new `main' function has external linkage

llvm-svn: 7371