Emscripten: Enable de-duplication of libraries for CMP0156 with LLD

LLD automatically resolves newly encountered symbols using object files
previously encountered.  Also, the Emscripten compiler driver invokes
the LLD linker with `--whole-archive ... --no-whole-archive` around all
the libraries.  Therefore we should not repeat any.

Issue: #27232
Suggested-by: Marc Chevrier <marc.chevrier@gmail.com>