* New Recursive Target: clean-all. This target will recursively descend the

  $(ObjDir) and clean out all build modes (Debug, Release, Profile) in
  addition to the normal "clean" rules.
* Fix "clean" problems with Lex/Yacc so all files are remove properly.
* Ensure errors from "rm" don't thwart the uninstall and clean targets.

llvm-svn: 17433