meson: Add valgrind test setup

Similarly to libtools, add a test setup to meson so that tests
can be run under valgrind even with meson:

  meson test -C $builddir --setup valgrind

Since meson has a timeout for individual tests (30 seconds) and
valgrind makes everything run slower, the timeout needs to be
increased (factor of 4 looks good enough).

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

meson.build

@@ -532,6 +532,15 @@ foreach check, deps : checks
     endif
 endforeach
 
+add_test_setup(
+  'valgrind',
+  exe_wrapper: [
+    'valgrind', '--quiet', '--leak-check=full', '--error-exitcode=1',
+  ],
+  # default timeout in meson is 30s
+  timeout_multiplier: 4,
+)
+
 if want_output
     sh = find_program('sh', required: false)