There's a few places in the Xorg code where the S_IF* macros are misused, such
as this check in xc/lib/X11/XKBCvt.c:
     if ( (stat(cf,&sbuf)==0) && (sbuf.st_mode&S_IFREG) &&

S_IF* are not pure bitmasks, but values to be compared with mode & S_IFMT.

For instance, on Solaris the values include:
#define S_IFREG         0x8000  /* regular */
#define S_IFLNK         0xA000  /* symbolic link */
#define S_IFSOCK        0xC000  /* socket */
#define S_IFDOOR        0xD000  /* door */
#define S_IFPORT        0xE000  /* event port */

which will all pass the above test as "regular files".

On FreeBSD, these values would pass that test:
#define S_IFREG  0100000                /* regular */
#define S_IFLNK  0120000                /* symbolic link */
#define S_IFSOCK 0140000                /* socket */
#define S_IFWHT  0160000                /* whiteout */

Fortunately, most of the places this is misused is in old code not used any
more since there are #ifdef's to use the OS-provided macros that do the right 
thing if they're available (such as this snippet from xc/lib/Xt/Intrinsic.c
that does the right thing on platforms without X_NOT_POSIX defined):

#ifndef X_NOT_POSIX
            S_ISDIR(status.st_mode) == 0);      /* not a directory */
#else
            (status.st_mode & S_IFDIR) == 0);   /* not a directory */
#endif /* X_NOT_POSIX else */

Offenders found by a find | xargs grep of the Xorg monolith were:
./config/util/checktree.c:    if ((fs->st_mode & S_IFLNK) == S_IFLNK) {
./config/util/checktree.c:    if ((fs->st_mode & S_IFDIR) == S_IFDIR) {
./config/util/checktree.c:    } else if ((fs->st_mode & S_IFREG) != S_IFREG)
./config/util/checktree.c:      if ((fs.st_mode & S_IFDIR) == S_IFDIR) {
./config/util/lndir.c:      if (sb.st_mode & S_IFDIR) 
./config/util/lndir.c:    if (!(ts.st_mode & S_IFDIR))
./config/util/lndir.c:    if (!(fs.st_mode & S_IFDIR))
./lib/X11/XKBCvt.c:     if ( (stat(cf,&sbuf)==0) && (sbuf.st_mode&S_IFREG) &&
./lib/Xt/Intrinsic.c:       (status.st_mode & S_IFDIR) == 0);   /* not a
directory */

checktree appears to be a no longer used distcheck tool for the old monolith
releases and can be ignored.

lndir uses the S_IS* macros instead if they are defined.

The XKBCvt.c is thus the only one we really need to fix, since most modern
platforms have S_IS*, but since it's trivial to fix lndir & Intrinsic.c as
well, a patch to fix all three will follow shortly.   (Will wait to commit
until after RC2 releases are tagged and released.)