Enable optional valgrind for testsuite
* configure.ac: Enable gnulib valgrind module. * gl/m4/gnulib.m4: Enable valgrind module. * tests/Makefile.am: Enable valgrind as LOG_COMPILER. * gl/m4/valgrind-tests.m4: New
- Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>