shift-count-overflow possible issue on 64bit type

[Jonny Grant]

I see on my 64bit Ubuntu PC that size_t is 8 bytes, that is 64bits, 
however I see a warning:

$ g++-8 -Wall -Wextra -o size_t size_t.cpp
size_t.cpp: In function ‘int main()’:
size_t.cpp:11:21: warning: left shift count >= width of type 
[-Wshift-count-overflow]
      size_t big = 1<<40;
                      ^~



Same on Godbolt trunk.
Is this an issue?

Regards, Jonny

https://godbolt.org/z/xeefQ8

#include <stdio.h>
size_t big = 1<<41;



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Jonny