Migrate the codegen code from BlockStmt to the new Loop ASTs
Add some printfs to verify that the LLVM BlockStmt::codegen() isn't being used for Loops
Merge pull request #672 from noakesmichael/loopWrap-2

Move loop codegen from BlockStmt to new AST nodes

Compiled: STD clang on mac, STD gnu on linux, LLVM gnu on linux
Tested: Full paratest with STD --verify and LLVM --verify
Reviewed: None