S_ISSOCK isn't defined on BeOS.

xpcom/io/nsLocalFileUnix.cpp

@@ -1296,7 +1296,9 @@ nsLocalFile::IsSpecial(PRBool *_retval)
     VALIDATE_STAT_CACHE();
     *_retval = S_ISCHR(mCachedStat.st_mode)      ||
                  S_ISBLK(mCachedStat.st_mode)    ||
+#ifdef S_ISSOCK
                  S_ISSOCK(mCachedStat.st_mode)   ||
+#endif
                  S_ISFIFO(mCachedStat.st_mode);
 
     return NS_OK;