See email thread starting here: https://www.sourceware.org/ml/binutils/2018-01/msg00001.html
include * coff/msdos.h: New header.
* coff/pe.h: Move common defines to msdos.h.
* coff/powerpc.h: Likewise.
bfd * i386msdos.c (msdos_mkobject); New function.
(msdos_object_p): New function.
(i386_msdos_vec): Use msdos_object_p as the check_format
function.
* peicode.h: Rename external_PEI_DOS_hdr, DOSMAGIC, and
NT_SIGNATURE to external_DOS_hdr, IMAGE_DOS_SIGNATURE, and
IMAGE_NT_SIGNATURE.
* peXXigen.c: Likewise.
* coff-ia64.c: Likewise.
Alan Modra
Zebediah Figura