posix.cfg: Warn in case the return value of localtime() is ignored. (#5555)

cfg/posix.cfg

@@ -4054,6 +4054,7 @@ The function 'mktemp' is considered to be dangerous due to race conditions and s
     <noreturn>false</noreturn>
     <returnValue type="struct tm *"/>
     <leak-ignore/>
+    <use-retval/>
     <arg nr="1" direction="in">
       <not-null/>
       <not-uninit/>

test/cfg/posix.c

@@ -30,6 +30,7 @@
 #include <stdarg.h>
 #include <ctype.h>
 #include <stdbool.h>
+#include <time.h>
 #if !(defined(__APPLE__) && defined(__MACH__))
 #include <mqueue.h>
 #endif
@@ -169,6 +170,14 @@ void invalidFunctionArgStr_mbsnrtowcs(void)
     if (mbsnrtowcs (wenough, &cp, 1, 10, &s) != 1 || wcscmp (wenough, L"AEF") != 0) {}
 }
 
+struct tm * ignoredReturnValue_localtime(const time_t *tp)
+{
+    // cppcheck-suppress [ignoredReturnValue,localtimeCalled]
+    localtime(tp);
+    // cppcheck-suppress localtimeCalled
+    return localtime(tp);
+}
+
 int nullPointer_getpwuid_r(uid_t uid, struct passwd *pwd, char *buffer, size_t bufsize, struct passwd **result)
 {
     // cppcheck-suppress nullPointer