[ELF] Move --print-map(-M)/--cref before checkSections() and openFile()

-M output can be useful when diagnosing an "error: output file too large" problem (emitted in openFile()).

I just ran into such a situation where I had to debug an erronerous
Linux kernel linker script. It tried to create a file larger than
INT64_MAX bytes.

This patch could have helped https://bugs.llvm.org/show_bug.cgi?id=44715 as well.

Reviewed By: grimar

Differential Revision: https://reviews.llvm.org/D75966