same problem that ed had, mktemp and fopen. see also OpenBSD's bug #150 
(http://cvs.openbsd.org/cgi-bin/wwwgnats.pl/full/150)

fileio.c:

                add_pathsep(itmp);
            STRCAT(itmp, TEMPNAME);
            if ((p = vim_strchr(itmp, '?')) != NULL)
                *p = extra_char;
3121:       if (mktemp((char *)itmp) == NULL)
                continue;
            return vim_strsave(itmp);

fopen problem:

mch_fopen is defined in macros.h for non VMS systems:

92:  # define mch_fopen(n, p)  fopen(vms_fixfilename(n), (p))

grepping in the vim-5.7 source:

edit.c:1799:        fp = mch_fopen((char *)files[i], "r");  /* open 
dictionary f
ile */
eval.c:2677:    if (*p && !mch_isdir(p) && (fd = mch_fopen((char *)p, "r")) 
!= N
ULL)
ex_cmds.c:1265:    if ((fp = mch_fopen((char *)file, READBIN)) == NULL)
ex_cmds.c:1314: fp_in = mch_fopen((char *)file, READBIN);
ex_cmds.c:1327:     fp_out = mch_fopen((char *)file, WRITEBIN);
ex_cmds.c:1449:         fp_out = mch_fopen((char *)tempname, WRITEBIN);
ex_cmds.c:1459:                 fp_out = mch_fopen((char *)tempname, 
WRITEBIN);
ex_cmds.c:3868:     if ((helpfd = mch_fopen((char *)p_hf, READBIN)) == 
NULL)
ex_docmd.c:4398:    cookie.fp = mch_fopen((char *)fname_exp, READBIN);
ex_docmd.c:4415:            cookie.fp = mch_fopen((char *)fname_exp, 
READBIN);
ex_docmd.c:6973:    if ((fd = mch_fopen((char *)eap->arg, mode)) == NULL)
getchar.c:969:    if ((scriptin[curscript] = mch_fopen((char *)NameBuff, 
READBIN
)) == NULL)
macros.h:86:# define mch_fopen(n, p)  fopen(vms_fixfilename(n), (p))
macros.h:92:# define mch_fopen(n, p)  fopen((n), (p))
main.c:723:                 if ((scriptin[0] = mch_fopen(argv[0], READBIN)) 
== N
ULL)
main.c:773:                 if ((scriptout = mch_fopen(argv[0],
memline.c:3347:     dummyfd = mch_fopen((char *)buf->b_fname, "w");
misc1.c:5719:    fd = mch_fopen((char *)tempname, "r");
os_unix.c:3481:    fd = fopen((char *)tempname, "r");
osdef1.h.in:19:extern FILE      *fopen __ARGS((char *, char *));
quickfix.c:160:    if ((fd = mch_fopen((char *)efile, "r")) == NULL)
search.c:3361:          if ((files[depth + 1].fp = mch_fopen((char 
*)new_fname,
"r"))
tag.c:1039:         if ((fp = mch_fopen((char *)tag_fname, "r")) == NULL)
tag.c:1223:                             fp = mch_fopen((char 
*)fullpath_ebuf, "r
");
termlib.c:115:    if (!(termcap = mch_fopen(tcap, "r")))