posix.cfg: Added support for dirfd().

cfg/posix.cfg

@@ -480,6 +480,17 @@ The obsolescent function 'usleep' is called. POSIX.1-2001 declares usleep() func
       <not-uninit/>
     </arg>
   </function>
+  <!-- http://man7.org/linux/man-pages/man3/dirfd.3.html -->
+  <!-- int dirfd(DIR *dirp); -->
+  <function name="dirfd">
+    <noreturn>false</noreturn>
+    <leak-ignore/>
+    <returnValue type="int"/>
+    <arg nr="1" direction="in">
+      <not-uninit/>
+      <not-null/>
+    </arg>
+  </function>
   <!-- http://man7.org/linux/man-pages/man2/access.2.html -->
   <!-- int faccessat(int dirfd, const char *pathname, int mode, int flags); -->
   <function name="faccessat">