distlinksbrk.test: Work around botched "make -k".

distlinksbrk.test: Work around botched "make -k".

* tests/distlinksbrk.test: Run "make" multiple times and grep
its output each time for a single error message, rather than
running "make -k" one single time and grepping its output for
all the expected error messages.  This should work around make
implementations with limited (broken?) `-k' support; for more
information, see these subthreads on the automake-patches list:
  - 2010-11-15, "Testsuite failures on HP-UX 11.23",
    <http://lists.gnu.org/archive/html/automake-patches/2010-11/msg00162.html>
  - 2010-11-15, "Testsuite failures on IRIX 6.5",
    <http://lists.gnu.org/archive/html/automake-patches/2010-11/msg00166.html>