PR 58148 patch

[François Dumont]

Hi

     The problem exposed in PR 58148 is quite trivial, std::common_type 
cannot find a result when instantiated with char* and const wchar_t*. 
The attached patch will fix this problem by dealing with a 
std::common_type resolution failure even if the drawback is that 
following call won't be detected as an invalid one anymore:

   std::vector<int> v;
   ....
   v.insert(v.begin(), reinterpret_cast<char*>(v.data() + 1), 
reinterpret_cast<char*>(v.data() + 5)); // Expected failure

     So I wonder why we can't simply use std::less<const volatile void*> 
and std::greater_equal<const volatile void*> ? Would there be any 
portability issue ? I remember that in the past a function pointer could 
not be casted to void* but I don't think it is still true. And even if 
it is so I can simply check that the result of the std::addressof call 
can be passed transparently as const volatile void*.

François

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