[PWGCF] Add custom event selection to energyFlowGfw.cxx

[EmilGorm]

No description provided.

[github-actions]

O2 linter results: ❌ 0 errors, ⚠️ 8 warnings, 🔕 0 disabled

[alibuild]

Auto-approving on behalf of @EmilGorm.

[alibuild]

Error while checking build/O2Physics/code-check for ae4253f at 2026-10-20 20:42:

## sw/BUILD/O2Physics-latest/log
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

Full log here.

[alibuild]

Error while checking build/O2Physics/o2 for ae4253f at 2026-10-20 20:46:

## sw/BUILD/O2Physics-latest/log
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

Full log here.

[alibuild]

Error while checking build/O2Physics/staging for ae4253f at 2026-10-20 21:30:

## sw/BUILD/O2Physics-latest/log
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

Full log here.

[vkucera]

Hi @EmilGorm , your PR does not compile on any platform. How did you test it?

[EmilGorm]

Hi @EmilGorm , your PR does not compile on any platform. How did you test it?

I only ran a compile check for the modified file, but I see now that there is a linker error that I hadn't caught. I fixed that now, and am checking the full O2Physics compilation before repushing.