bpo-40280: Emscripten has no support for subprocesses (GH-29872)

Fixes ``platform`` and ``help()`` on emscripten.

Signed-off-by: Christian Heimes <christian@python.org>

Automerge-Triggered-By: GH:tiran

Lib/pydoc.py

@@ -1556,6 +1556,8 @@ def getpager():
         return plainpager
     if not sys.stdin.isatty() or not sys.stdout.isatty():
         return plainpager
+    if sys.platform == "emscripten":
+        return plainpager
     use_pager = os.environ.get('MANPAGER') or os.environ.get('PAGER')
     if use_pager:
         if sys.platform == 'win32': # pipes completely broken in Windows