DIP(?) Warning to facilitate porting to other archs

[Temtaime via Digitalmars-d]

Hi everyone.
I think it's need to have -w64(or other name, offers ?) flag that 
warns if code may not compile on other archs.

Example:
size_t a;
uint b = a; // ok on 32 without a warning but fail on 64 with 
error

And on 32 with -w64 it'll be :
Warning : size_t.sizeof may be greater than 32 bit

What you thinks ?
Should i create proposal or nobody cares about porting and it's 
useless ?

Any ideas are welcome.