See JDK-8352689 for a use-case where this would be useful. Consider a JDK built in an RPM and JEP 493 enabled (using --enable-linkable-runtime). Then it would be useful to also be able to add extra jlink flags during the JDK build. For example, to solve the full RPM and debug symbols stripping issue with JEP 493 enabled JDKs, one could use this combination of configure option to achieve the desired result:

--enable-linkable-runtime --with-extra-jlink-flags="--save-jlink-argfiles /path/to/jlink-args-file"

The jlink arg file could add the extra needed jlink arguments to supply alternative hash sums of RPM-stripped binaries and libraries.