Check if the target is running on DOS. DOS doesn't allow a dot as
the first character, more than one dot, more than eight characters
before a dot, and just three letters after the dot. A DOS VM
running under Windows 9X does not have these restrictions. A DOS
program can be running in either environment, so its important to
code accordingly. Defines HAVE_DOS_FILESYS_LIMITATIONS if under
Use in conjunction with ACX_CHECK_PATHNAME_STYLE_DOS.