bug#25912: 2.1.7 segfaults on cygwin

[Mike Gran]

Hi-
I also can replicate the Cygwin problem as originally described.
After wingo's comment on the mmap path vs the non-mmap path,
I tried to use the non-mmap path by removing HAVE_SYS_MMAN_H
from the config.h.
The non-mmap path doesn't build.  The errors are in map_file_contents()
in loader.c
Making the obvious patches to map_file_contents() does
seem to allow the Cygwin build to continue.
The helper functions sniff_elf_alignment and copy_and_align_elf_data
are no longer included in master and had to be pulled from an older
rev.
Regards,
Mike