Add <limits.h> integer width macros

[Paul Eggert]

On 09/16/2016 05:32 PM, Paul Eggert wrote:
> the patch looks good; thanks.

Unfortunately I did not check the patch thoroughly enough, as the patch 
turns out to define LONG_WIDTH incorrectly on i686 with 
gcc-6.2.1-2.fc26.i686, and this causes grep's 'make check' to fail 
(luckily these are side tests; grep itself works fine). See:

https://bugzilla.redhat.com/show_bug.cgi?id=1381582