posix.cfg: Added support for mkdirat().

cfg/posix.cfg

@@ -885,6 +885,24 @@ The function 'mktemp' is considered to be dangerous due to race conditions and s
       <not-bool/>
     </arg>
   </function>
+  <!-- int mkdirat(int dirfd, const char *pathname, mode_t mode); -->
+  <function name="mkdirat">
+    <noreturn>false</noreturn>
+    <returnValue type="int"/>
+    <leak-ignore/>
+    <arg nr="1" direction="in">
+      <not-uninit/>
+      <valid>0:</valid>
+    </arg>
+    <arg nr="2" direction="in">
+      <not-null/>
+      <not-uninit/>
+    </arg>
+    <arg nr="3" direction="in">
+      <not-uninit/>
+      <not-bool/>
+    </arg>
+  </function>
   <!-- int rmdir(const char *pathname); -->
   <function name="rmdir">
     <noreturn>false</noreturn>