gnu.cfg: Added support fo xexit().

cfg/gnu.cfg

@@ -13,6 +13,13 @@
     <alloc init="true">xcalloc</alloc>
     <dealloc>free</dealloc>
   </memory>
+  <!-- void xexit(int status); -->
+  <function name="xexit">
+    <noreturn>true</noreturn>
+    <arg nr="1">
+      <not-uninit/>
+    </arg>
+  </function>
   <!-- void * xmalloc(size_t size); -->
   <function name="xmalloc">
     <use-retval/>