Compile of empty file fails with typescript generation enabled

`touch main.cpp` (empty file)
`emcc --embind-emit-tsd a.d.ts -g -lembind main.cpp -o a.out.html`

I get:
`error: undefined symbol: ___getTypeName (referenced by root reference (e.g. compiled C/C++ code))`

/cc @sbc100 maybe another linker issue?