QV4_PROFILE_WRITE_PERF_MAP no longer working

The QML/JS engine had the feature to write a perf map file for all its JIT-compiled JS functions. This could be turned on with QV4_PROFILE_WRITE_PERF_MAP=1.

This feature seems to no longer exist.

A workaround to still record usable perf traces is to disable the JIT compiler with QV4_FORCE_INTERPRETER=1. However that changes the result as it slows down code execution - and for profiling, one should always measure as close to a normal execution as possible.

Note that this is documented to work on https://doc.qt.io/qtcreator/creator-cpu-usage-analyzer.html.