Reduce -Wuninitialized time by 22% (on sqlite) by removing the recursive AST crawl.

This is accomplished by forcing the needed expressions for -Wuninitialized to always be CFGElements in the CFG.
This allows us to remove a fair amount of the code for -Wuninitialized.

Some fallout:
- AnalysisBasedWarnings.cpp now specifically toggles the CFGBuilder to create a CFG that is suitable for -Wuninitialized.  This
is a layering violation, since the logic for -Wuninitialized is in libAnalysis.  This can be fixed with the proper refactoring.
- Some of the source locations for -Wunreachable-code warnings have shifted.  While not ideal, this is okay because that analysis
already needs some serious reworking.

llvm-svn: 135480
4 files changed
tree: 020c8bb3ad7b4dfed63a46874f883442f1adb693
  1. clang/
  2. compiler-rt/
  3. debuginfo-tests/
  4. libcxx/
  5. libcxxabi/
  6. lldb/
  7. llvm/
  8. polly/