RISC-V XRay missing _xray_ArgLoggerEntry implementation

Commit c6f501d479e8 fixed an issue where some tests were incorrectly marked as unsupported for a bootstrapping build. This exposed on our bootstrap builder that fdr-mode.cpp actually fails at RISC-V, I believe because we miss an `_xray_ArgLoggerEntry`.

This issue is being filed so it's at least noted and can be tracked. The test has been marked as UNSUPPORTED for now, so there is no immediate need to address in any other way.

Start with fdr-mode.cpp and reproduce the failure on the RISC-V bootstrap builder, then inspect the XRay code related to _xray_ArgLoggerEntry. The issue is complete when the RISC-V failure is addressed and the affected test no longer needs its UNSUPPORTED marking.

Written by the indexing model from the issue text.