Fix regcomp.c build for 32-bit with GCC mainline

[Joseph Myers]

On Mon, 20 Nov 2017, Adhemerval Zanella wrote:

> Why not use the already upstream fix from gnulib 
> (252b52457da7887667c036d18cc5169777615bb0) ?

That change would not apply cleanly to current sources, and if we have 
over five years of regex changes out of sync with gnulib, it doesn't seem 
a good idea to try to tie any possible resync with gnulib (in both 
directions) to fixing build failures to make it possible to detect build 
regressions when they occur (rather than piling one failure on top of 
another that isn't yet fixed, so making it hard to determine the 
problematic patch, which is the current state).

-- 
Joseph S. Myers
joseph@codesourcery.com