Warn about usage of posix function mktemp (#3918).

Author: PKEuS

cfg/posix.cfg

@@ -528,6 +528,8 @@ The obsolescent function 'usleep' is called. POSIX.1-2001 declares usleep() func
       <not-null/>
       <not-uninit/>
     </arg>
+    <warn severity="warning">Obsolete function 'mktemp' called. It is recommended to use 'mkstemp' or 'mkdtemp' instead.
+The function 'mktemp' is considered to be dangerous due to race conditions and some implementations generating only up to 26 different filenames out of each template. This function has been removed in POSIX.1-2008. Use 'mkstemp' or 'mkdtemp' instead.</warn>
   </function>
   <!-- char *getcwd(char *buf, size_t size); -->
   <function name="getcwd">