Possible codegen issue with Deno

[rsms]

See https://github.com/rsms/markdown-wasm/issues/6

It appears as Emscripten generates the following code:

if (ENVIRONMENT_IS_WEB || ENVIRONMENT_IS_WORKER) {
  // ...
  if (document.currentScript) {
  // ...

which when executed in Deno causes a crash (since there's no document in deno.) The above code is fenced (again, by emscripten) by the following constants:

ENVIRONMENT_IS_WEB = typeof window === "object";
ENVIRONMENT_IS_WORKER = typeof importScripts === "function";
ENVIRONMENT_IS_NODE = ENVIRONMENT_HAS_NODE && !ENVIRONMENT_IS_WEB && !ENVIRONMENT_IS_WORKER;

wasmc overrides ENVIRONMENT_IS_WEB only when target:"web" is explicitly defined in a wasmc.js file

Note: This may turn out to be a non-issue. Just filing so to remember to check it out.