[llvm-objcopy][ELF] Allow --dump-section to dump an empty non-SHT_NOBITS section

This is the ELF part of D75949.

GNU objcopy from binutils 2.35 onwards will support an empty non-SHT_NOBITS section as
well
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=e052e2ba295a65b6ea80cbc3f90495beca299c42

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D79339