Prevent eclipse from building the projects before run an Ant task

In newer versions of Eclipse (I have Neon) the option has moved slightly to:

Window > Preferences > Run/Debug > Launching

The checkbox is still named: Build (if required) before launching.

You can turn off "Build (if required) before launch"

You have turned rebuild off for resource modification but I believe you haven't turned off "Build (if required) before launch"

Go to:

Window > Preferences > Run/Debug > Launching -> Build (if required) before launching

On older versions of eclipse:

Window > Preferences > Run/Debug > Build (if required) before launching