[glibc] Copy regex_internal.h from Gnulib

[Paul Eggert <eggert@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=2cc478ed1be82711a6cac15aae683530b2e6732b

commit 2cc478ed1be82711a6cac15aae683530b2e6732b
Author: Paul Eggert <eggert@cs.ucla.edu>
Date:   Tue Aug 4 23:45:27 2020 -0700

    Copy regex_internal.h from Gnulib
    
    Sync this file from Gnulib, thus incorporating the following
    fix for a bug with regexps with 16 or more subexpressions:
    * posix/regex_internal.h (struct re_backref_cache_entry):
    Use bitset_word_t as the type of eps_reachable_subexps_map,
    instead of unsigned short int.  This fixes a bug I introduced
    to glibc in 2005-09-28T17:33:18Z!drepper@redhat.com (glibc commit
    2c05d33f90861d074dc12808dafbde30f487b1a0, BZ #1302).
    Remove unused member 'unused'.

Diff:
---
 posix/regex_internal.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/posix/regex_internal.h b/posix/regex_internal.h
index e9aa74bf33..8c42586c42 100644
--- a/posix/regex_internal.h
+++ b/posix/regex_internal.h
@@ -591,9 +591,8 @@ struct re_backref_cache_entry
   Idx str_idx;
   Idx subexp_from;
   Idx subexp_to;
+  bitset_word_t eps_reachable_subexps_map;
   char more;
-  char unused;
-  unsigned short int eps_reachable_subexps_map;
 };
 
 typedef struct