Changes for VLA warnings, and some more warning fixes

Hello Stephen,

In this patch-set I have some changes I cooked up that, as you recommended, turn the VLA warning back on and replace usage of it in ClangASTContext with an llvm::SmallVector. It also cleans up some miscellaneous warnings, but you may have already fixed these in some other way perhaps. With your latest changes I pulled in, LLDB is now compiling pretty close to warning free it seems which is great! I'll probably have a few more warning fixes etc. I want you to pull in before too long (and if you'd rather I send these to the lldb-commits list, just let me know.)

Please pull.