This patch changes llvm-readelf (and llvm-readobj for consistency)
behavior to print an error when executed with no input files.
Reading from stdin can be achieved via a '-' for the input
object.
Fixes https://bugs.llvm.org/show_bug.cgi?id=46400
Differential Revision: https://reviews.llvm.org/D83704
Reviewed by: jhenderson, MaskRay, sbc, jyknight