Currently Sparse-LLVM outputs the generated LLVM bitcode file to stdout. While this works, it means that a) users cannot just run sparse-llvm and get any meaningful help on stdout - instead you get lot of gibberish, and b) it is somewhat unusual behaviour for a 'compiler'. 

I suggest adding a -o option to output to a named file. Additionally keeping with most compiler behaviour, if no option is specified, create 'out.bc' file instead of writing to stdout.

I can submit patches for this if there is agreement on the approach. Please give feedback or let me know if you approve / disapprove.