Make default release mode build a "profiling" build

For the ability to profile our code with perf (and to generate the most readable flamegraphs) it is important to:

• Compile with -fno-omit-frame-pointer (unless the compiler already defaults to using this flag?)
• Compile with some debug symbols (unless you don't need detailed stack traces of your node module)

Doing this would move node-cpp-skel to doing a "profiling" build by default: https://github.com/mapbox/cpp/blob/master/glossary.md#profiling-build.

We can accomplish this by applying something like https://github.com/mapnik/node-mapnik/pull/804 to node-cpp-skel.

refs https://twitter.com/brendangregg/status/472869470675795968

Untersuche die standardmäßige Release-Build-Konfiguration des Repositorys und vergleiche anschließend den gewünschten Ansatz mit node-mapnik PR #804. Bestätige, dass der Standard-Build -fno-omit-frame-pointer verwendet und Debug-Symbole enthält, und überprüfe, dass das resultierende Node-Modul weiterhin gebaut werden kann und für perf-Flamegraphs geeignet ist.