Support mcel API in remaining modules where this might matter,
for apps that prefer it.
* lib/mbmemcasecmp.c, lib/mbscspn.c, lib/mbsncasecmp.c, lib/mbsnlen.c:
* lib/mbspbrk.c, lib/mbspcasecmp.c, lib/mbssep.c, lib/mbsspn.c:
* lib/regex-quote.c:
Include mcel.h instead of mbiterf.h or mbuiterf.h,
if GNULIB_MCEL_PREFER.
* lib/mbmemcasecmp.c (mbmemcasecmp), lib/mbscspn.c (mbscspn):
* lib/mbsncasecmp.c (mbsncasecmp), lib/mbsnlen.c (mbsnlen):
* lib/mbspbrk.c (mbspbrk), lib/mbspcasecmp.c (mbspcasecmp):
* lib/mbssep.c (mbssep), lib/mbsspn.c (mbsspn):
* lib/regex-quote.c (regex_quote_length, regex_quote_copy):
Use mcel API, if GNULIB_MCEL_PREFER.
* lib/mbscspn.c, lib/mbspbrk.c, lib/mbspcasecmp.c, lib/mbsspn.c:
Include stdlib.h, for MB_CUR_MAX.
* modules/mbmemcasecmp, modules/mbsncasecmp, modules/mbspcasecmp:
Depend on c32tolower.
* modules/regex-quote: Depend on mempcpy.