Fix link errors on platforms with libunistring.

Fix link errors on platforms with libunistring.

* modules/c32isalnum (Link): New section.
* modules/c32isalnum-tests (Makefile.am): Link test-c32isalnum with
$(LIBUNISTRING).
* modules/c32isalpha (Link): New section.
* modules/c32isalpha-tests (Makefile.am): Link test-c32isalpha with
$(LIBUNISTRING).
* modules/c32isblank (Link): New section.
* modules/c32isblank-tests (Makefile.am): Link test-c32isblank with
$(LIBUNISTRING).
* modules/c32iscntrl (Link): New section.
* modules/c32iscntrl-tests (Makefile.am): Link test-c32iscntrl with
$(LIBUNISTRING).
* modules/c32isdigit (Link): New section.
* modules/c32isdigit-tests (Makefile.am): Link test-c32isdigit with
$(LIBUNISTRING).
* modules/c32isgraph (Link): New section.
* modules/c32isgraph-tests (Makefile.am): Link test-c32isgraph with
$(LIBUNISTRING).
* modules/c32islower (Link): New section.
* modules/c32islower-tests (Makefile.am): Link test-c32islower with
$(LIBUNISTRING).
* modules/c32isprint (Link): New section.
* modules/c32isprint-tests (Makefile.am): Link test-c32isprint with
$(LIBUNISTRING).
* modules/c32ispunct (Link): New section.
* modules/c32ispunct-tests (Makefile.am): Link test-c32ispunct with
$(LIBUNISTRING).
* modules/c32isspace (Link): New section.
* modules/c32isspace-tests (Makefile.am): Link test-c32isspace with
$(LIBUNISTRING).
* modules/c32isupper (Link): New section.
* modules/c32isupper-tests (Makefile.am): Link test-c32isupper with
$(LIBUNISTRING).
* modules/c32isxdigit (Link): New section.
* modules/c32isxdigit-tests (Makefile.am): Link test-c32isxdigit with
$(LIBUNISTRING).
* modules/unicodeio (Link): Mention $(LIBUNISTRING).
* modules/unicodeio-tests (Makefile.am): Link test-unicodeio with
$(LIBUNISTRING).