build-sys: fix valgrind-tests

Fixes:
```
$ make valgrind-tests TESTS=test-acl-util
  GEN      valgrind-tests
  Running test-acl-util
  /bin/bash: line 4: libtool: command not found
```

diff --git a/Makefile.am b/Makefile.am
index 00a92e3..3516b50 100644 (file)
--- a/Makefile.am
+++ b/Makefile.am
@@ -6292,7 +6292,7 @@ valgrind-tests: $(TESTS)
                if file $$f | grep -q shell; then \
                echo -e "$${x}Skipping non-binary $$f"; else \
                echo -e "$${x}Running $$f"; \
-               libtool --mode=execute valgrind -q --leak-check=full --max-stackframe=5242880 --error-exitcode=55 $(builddir)/$$f ; fi; \
+               $(LIBTOOL) --mode=execute valgrind -q --leak-check=full --max-stackframe=5242880 --error-exitcode=55 $(builddir)/$$f ; fi; \
                x="\n\n"; \
        done