tools: Allow running tests with valgrind.

tools/runtest

@@ -118,4 +118,10 @@ fi
 WINETEST_PLATFORM=${platform:-wine}
 export WINETEST_PLATFORM WINETEST_DEBUG
 
-exec "$topobjdir/wine" "$program" "$infile" "$@"
+# WINETEST_WRAPPER is normally empty, but can be set by caller, e.g.
+#  WINETEST_WRAPPER=time
+# would give data about how long each test takes, and
+#  WINETEST_WRAPPER=valgrind
+# would run the tests under valgrind to look for memory errors.
+
+exec $WINETEST_WRAPPER "$topobjdir/wine" "$program" "$infile" "$@"