Use POSIX macros for linux

cde/programs/dtfile/FileManip.c

@@ -55,7 +55,7 @@
 #    include <sys/fs/ufs_fs.h>
 #    define ROOTINO UFSROOTINO
 #else
-#  if defined(linux) || defined(CSRG_BASED)
+#  if defined(__linux__) || defined(CSRG_BASED)
 #    define ROOTINO 2
 #  endif
 #  include <sys/param.h>
@@ -975,7 +975,7 @@ FileManip(
    if (lstat (to, &s2) >= 0) 			   /* <to> exists */
    {
       if ((stat (to, &s3) >= 0) &&
-#if defined(__ultrix) || defined(linux) || \
+#if defined(__ultrix) || defined(__linux__) || \
 	defined(CSRG_BASED)
            (((s3.st_mode & S_IFMT) == S_IFDIR)          /* if is a directory */
            || ((s3.st_mode & S_IFMT) == S_IFSOCK)) )    /* or a net special */