1. Main include corresponding to .cpp file, if any.
2. DMD and LDC includes.
3. LLVM includes.
4. System includes.
Also updated a few include guards to match the default format.
- New functions codeGenOptLevel() and verifyModule() to remove code duplication
- Hidden option no-verify renamed to disable-verify and moved to optimizer (like opt tool)
- Removed global.params.noVerify