Tests/RunCMake/IAR: Add missing linker options for RH850

The initial implementation of the scripts driving nightly tests for IAR did not contain linker configuration options for RH850. Differently from (e.g.) ilinkarm, which offers fallback options for such requirements, ilinkrh850 is unable to link an executable without a minimal set of linker symbols.

This MR aims to provide the minimal set of parameters so that nightly tests can be performed.

Closes: #26249 (closed)