Prepare for LLVM 10 upgrade Split off from #67759, this just adds the necessary compatibility bits and updates codegen tests, without performing the actual LLVM upgrade. r? @alexcrichton
The codegen
crate contains the code to convert from MIR into LLVM IR,
and then from LLVM IR into machine code. In general it contains code
that runs towards the end of the compilation process.
For more information about how codegen works, see the rustc guide.