Reimplement the old and horrible bison parser for .ll files with a nice

Reimplement the old and horrible bison parser for .ll files with a nice
and clean recursive descent parser.

This change has a couple of ramifications:
1. The parser code is about 400 lines shorter (in what we maintain, not
   including what is autogenerated).
2. The code should be significantly faster than the old code because we
   don't have to work around bison's poor handling of datatypes with
   ctors/dtors.  This also makes the code much more resistant to memory
   leaks.
3. We now get caret diagnostics from the .ll parser, woo.
4. The actual diagnostics emited from the parser are completely different
   so a bunch of testcases had to be updated.
5. I now disallow "%ty = type opaque %ty = type i32".  There was no good
   reason to support this, it was just an accident of the old
   implementation.  I have no reason to think that anyone is actually using
   this.
6. The syntax for sticking a global variable has changed to make it
   unambiguous.  I don't think anyone is depending on this since only clang
   supports this and it is not solid yet, so I'm not worried about anything
   breaking.
7. This gets rid of the last use of bison, and along with it the .cvs files.
   I'll prune this from the makefiles as a subsequent commit.

There are a few minor cleanups that can be done after this commit (suggestions
welcome!) but this passes dejagnu testing and is ready for its time in the
limelight.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61558 91177308-0d34-0410-b5e6-96231b3b80d8