Use proper LLVM API for naming structs

Signed-off-by: Pekka Enberg <penberg@iki.fi>
Fix GetElementPtrInstr::Create LLVM API call

Signed-off-by: Pekka Enberg <penberg@iki.fi>
test: Fix 64-bit type and printf format issues

Signed-off-by: Pekka Enberg <penberg@iki.fi>