tests: Fix link errors on Solaris, when libunistring-optional is in use.

tests: Fix link errors on Solaris, when libunistring-optional is in use.

* modules/wcwidth (Link): New section.
* modules/wcswidth (Link): New section.
* modules/mbchar (Link): New section.
* modules/mbfile (Link): Link against libunistring.
* modules/mbiter (Link): Likewise.
* modules/mbuiter (Link): Likewise.
* modules/mbmemcasecmp (Link): Likewise.
* modules/mbscasecmp (Link): Likewise.
* modules/mbscasestr (Link): Likewise.
* modules/mbschr (Link): Likewise.
* modules/mbscspn (Link): Likewise.
* modules/mbslen (Link): Likewise.
* modules/mbsncasecmp (Link): Likewise.
* modules/mbsnlen (Link): Likewise.
* modules/mbspbrk (Link): Likewise.
* modules/mbspcasecmp (Link): Likewise.
* modules/mbsrchr (Link): Likewise.
* modules/mbssep (Link): Likewise.
* modules/mbsspn (Link): Likewise.
* modules/mbsstr (Link): Likewise.
* modules/mbstok_r (Link): Likewise.
* modules/mbswidth (Link): Likewise.
* modules/exclude (Link): Likewise.
* modules/propername (Link): Likewise.
* modules/regex-quote (Link): Likewise.
* modules/trim (Link): Likewise.
* modules/mbmemcasecmp-tests (Makefile.am): Link the test program
against libunistring.
* modules/mbscasecmp-tests (Makefile.am): Likewise.
* modules/mbscasestr-tests (Makefile.am): Likewise.
* modules/mbschr-tests (Makefile.am): Likewise.
* modules/mbscspn-tests (Makefile.am): Likewise.
* modules/mbsncasecmp-tests (Makefile.am): Likewise.
* modules/mbspbrk-tests (Makefile.am): Likewise.
* modules/mbspcasecmp-tests (Makefile.am): Likewise.
* modules/mbsrchr-tests (Makefile.am): Likewise.
* modules/mbsspn-tests (Makefile.am): Likewise.
* modules/mbsstr-tests (Makefile.am): Likewise.
* modules/exclude-tests (Makefile.am): Likewise.
* modules/regex-quote-tests (Makefile.am): Likewise.