[emscripten] add wasm32 build target

[ololoken]

it builds; it's runnable; but fails on race launch with err

Uncaught RuntimeError: null function or function signature mismatch
    at dethrace.wasm.V1Face_OS_Render (v1model.c:500:4)
    at dethrace.wasm.V1Model_Render (v1model.c:966:5)
    at dethrace.wasm._M_br_geometry_v1_model_soft_renderOnScreen (v1model.c:1013:6)
    at dethrace.wasm.renderFaces (modrend.c:34:4)
    at dethrace.wasm.BrDbModelRender (render.c:170:3)
    at dethrace.wasm.actorRender (render.c:368:4)
    at dethrace.wasm.actorRender (render.c:409:3)
    at dethrace.wasm.actorRender (render.c:409:3)
    at dethrace.wasm.BrZbSceneRenderAdd (render.c:603:3)
    at dethrace.wasm.main (graphics.c:1199:5)

Will try to debug on weekend. Working demo (also has some bugs) base of v0.8.0 https://turch.in/dethrace/index.html