std.cfg: Added more tests for some std::vector functions.

cfg/std.cfg

@@ -6056,6 +6056,7 @@ The obsolete function 'gets' is called. With 'gets' you'll get a buffer overrun
   </function>
   <function name="std::list::pop_back,std::list::pop_front,std::forward_list::pop_front,std::vector::pop_back">
     <noreturn>false</noreturn>
+    <returnValue type="void"/>
   </function>
   <function name="std::stack::pop,std::queue::pop">
     <noreturn>false</noreturn>

test/cfg/std.cpp

@@ -3267,7 +3267,18 @@ void stdstring()
 
 void stdvector()
 {
+    int uninit;
     std::vector<int> v;
     // cppcheck-suppress ignoredReturnValue
     v.size();
+    // cppcheck-suppress uninitvar
+    v.push_back(uninit);
+
+    // no warning is expected for pop_back()
+    v.push_back(42);
+    v.pop_back();
+
+    v.push_back(42);
+    // cppcheck-suppress ignoredReturnValue
+    v.back();
 }