WebAssembly: emsdk detection ceased working due to changes in emsdk activation

Qt Creator's automatic detection of the emsdk depends on the file ~/.emscripten being present and being parse-able.

Up to very recently, the only challenge to make this possible was to omit the -embedded parameter in the emsdk activate step.

However, it seems that now, embedded is the default, and there is no non-embedded option. Detection needs to be adapted perhaps by making it less automagic but let the user control it.