Enable assert in CodeGen.cpp

Hi

I found that assert is not working in CodeGen.cpp

As your comments note, assert is disabled by LLVM.  assert.h is reprocessed each time it is encountered, so llvm disables assert after Util.h enables it.  (Compilation environment: G++ 4.6 on Ubuntu)

Changes
1. Util.h: Move include of assert.h to front of Util.h so that each include of Util.h reincludes assert.h
2. CodeGen.cpp: Move include of Util.h after llvm includes that (may) disable assert.

Len Hamey
Macquarie University