Inliner: simple performance tests

Inliner: simple performance tests

Tests that demonstrate that constant arguments passed to callees can
lead to inlining performance wins. All numeric types are tested, as
well as strings.

Tests are generally written as positive/negative pairs with calls to
the same inlinee. This exposes the call site sensitivity. Performance
of the positive test should be better than the negative test.

The overall benchmarking approach used here is something that we might
consider adopting for other small-scale codegen performance tests.