gitignore: add perf/lua/Makefile

This is a follow-up for the commit
49d9a874 ("perf: add targets for running
Lua performance tests"), where the corresponding perf test target is
introduced.

NO_DOC=perf test
NO_CHANGELOG=perf test
NO_TEST=perf test

.gitignore

@@ -42,6 +42,7 @@ doc/*/Makefile
 extra/Makefile
 extra/*/Makefile
 perf/Makefile
+perf/lua/Makefile
 test/Makefile
 test/*/Makefile
 test/*/*/Makefile