The CoreName is set to CoreNG in the C/C++ Build>Build Variables.
Interestingly, when I added the quotes around the syscall.o path string, get –start-group ""
Hmm... what if,

Replaced
${workspace_loc:/${CoreName}/RADDS/cores/arduino/syscalls.o}

with
C:\Eclipse\Firmware\CoreNG\RADDS\cores\arduino/syscalls.o

Success!!! Generated bin file.
Funny, building Lars CoreXYU fork for Duet085 the string is:
${workspace_loc:/${CoreName}/SAM3X8E/cores/arduino/syscalls.o}
and builds fine.