[analyzer] Add system header simulator a symmetric random access iterator operator+

[gamesh411]

Summary

Random access iterators must handle operator+, where the iterator is on the
RHS. The system header simulator library is extended with these operators.

[Szelethus]

Yay!

clang/test/Analysis/Inputs/system-header-simulator-cxx.h

template <typename T, typename Ptr, typename Ref> struct __vector_iterator {
   __vector_iterator<T, Ptr, Ref> operator--() { -- ptr; return *this; }
   __vector_iterator<T, Ptr, Ref> operator--(int) {
     auto tmp = *this; -- ptr;
     return tmp;
   }
   __vector_iterator<T, Ptr, Ref> operator+(difference_type n) {
     return ptr + n;
   }
+  friend __vector_iterator<T, Ptr, Ref> operator+(
+      difference_type n,
+      const __vector_iterator<T, Ptr, Ref> &iter) {
+    return n + iter.ptr;
+  }
   __vector_iterator<T, Ptr, Ref> operator-(difference_type n) {
     return ptr - n;
   }
   __vector_iterator<T, Ptr, Ref> operator+=(difference_type n) {
     return ptr += n;
   }
   __vector_iterator<T, Ptr, Ref> operator-=(difference_type n) {
     return ptr -= n;
template <typename T, typename Ptr, typename Ref> struct __deque_iterator {
   __deque_iterator<T, Ptr, Ref> operator--() { -- ptr; return *this; }
   __deque_iterator<T, Ptr, Ref> operator--(int) {
     auto tmp = *this; -- ptr;
     return tmp;
   }
   __deque_iterator<T, Ptr, Ref> operator+(difference_type n) {
     return ptr + n;
   }
+  friend __deque_iterator<T, Ptr, Ref> operator+(
+      difference_type n,
+      const __deque_iterator<T, Ptr, Ref> &iter) {
+    return n + iter.ptr;
+  }
   __deque_iterator<T, Ptr, Ref> operator-(difference_type n) {
     return ptr - n;
   }
   __deque_iterator<T, Ptr, Ref> operator+=(difference_type n) {
     return ptr += n;
   }
   __deque_iterator<T, Ptr, Ref> operator-=(difference_type n) {
     return ptr -= n;

clang/test/Analysis/diagnostics/explicit-suppression.cpp

class C {
   // The virtual function is to make C not trivially copy assignable so that we call the
   // variant of std::copy() that does not defer to memmove().
   virtual int f();
 };
 
 void testCopyNull(C *I, C *E) {
   std::copy(I, E, (C *)0);
 #ifndef SUPPRESSED
-  // expected-warning@../Inputs/system-header-simulator-cxx.h:699 {{Called C++ object pointer is null}}
+  // expected-warning@../Inputs/system-header-simulator-cxx.h:709 {{Called C++ object pointer is null}}
 #endif
 }