[3.14] gh-127146: Report uid in Emscripten + node as native uid (GH-136509) (#136699)

Corrects the handling of getuid on emscripten, which was consistently reporting as 0.
(cherry picked from commit e81c4e84b3a8688a367099e3adf9b2fcf914447f)

Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>