[Bug c/61240] [4.8/4.9/4.10 Regression] Incorrect warning "integer overflow in expression" on pointer-pointer subtraction

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61240

--- Comment #7 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
But C++ has its own pointer_diff version that doesn't do such optimization. 
With my change the C FE would generate the same expr as the C++ FE.  And FEs
shouldn't perform such optimizations anyway.