[3.14] gh-145177: Add make-dependencies command to emscripten build script (GH-146158) (#146184)

Adds a standalone target for building all dependencies so that the buildbot
script is independent of a specific dependency list.
(cherry picked from commit db11623694d1231323ee3a9339f7f7504a839478)

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