regex: don't depend on wcscoll

* m4/regex.m4 (gl_PREREQ_REGEX): Don't check for wcscoll.
It is no longer used.
xfreopen: fix typo: s/frepoen/freopen/

* lib/xfreopen.c: Fix description.
* modules/xfreopen: Likewise.
regex: also remove dependency on HAVE_WCSCOLL

* lib/regex_internal.h: Remove final vestige of the wcscoll dependency.
selinux-h: really build without selinux when library is missing

* m4/selinux-selinux-h.m4: When the selinux library is missing, really
continue without selinux, as already told in the warning message.

This is necessary for when the 64bit selinux development package is
installed only, but the package (tar-1.27 fex) is built as 32bit,
causing the header files to be found while the library already wasn't
found earlier.