bpo-40280: Add build target for Emscripten/node.js

[emmatyping]

This adds a "python.js" target to the Makefile. We enable the raw
node.js filesystem mode as suggested by @thomasballinger as it will make running
the test suite under node easier, c.f.
emmatyping/python-wasm#36.

The wasm_asset.py script is updated to include the test module. Care is
taken to skip compiling the Python files that are examples of bad syntax
or encoding.

This also turns on memory growth as early into the test suite I was
running into OOMs.

cc @tiran

This requires my other PR to work of course #30494 (This is now merged)

https://bugs.python.org/issue40280

[emmatyping]

I'm unsure if this needs a NEWS entry, I'd be happy to add one if so.

[emmatyping]

This is the least intrusive way I could think of to customize the link step only for building the python.wasm executable...

If you know of a better way, please do tell :)

[tiran]

Meh! The ugly hacks are piling up. Maybe it's easier to not use ac_cv_pthread and to add -pthread to CFLAGS or CFLAGS_NODIST after all?

[emmatyping]

Unfortunately then it would be passed to the $(BUILDPYTHON) target, and standalone wasm doesn't support -pthread

[tiran]

I found a better way to deal with the issue. I guess you did the same mistake as I and added the skipif call after the check for AIX? That doesn't work because @requireSocket("AF_INET", "SOCK_STREAM", "IPPROTO_SCTP") tries to create an IPPROTO_SCTP socket and decorators are executed in reverse order!

This works:

--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -43,6 +43,7 @@
 
 VSOCKPORT = 1234
 AIX = platform.system() == "AIX"
+EMSCRIPTEN = sys.platform == "Emscripten"
 
 try:
     import _socket
...

 @requireAttrs(socket.socket, "sendmsg")
-@unittest.skipIf(AIX, "IPPROTO_SCTP: [Errno 62] Protocol not supported on AIX")
 @requireSocket("AF_INET", "SOCK_STREAM", "IPPROTO_SCTP")
+@unittest.skipIf(AIX, "IPPROTO_SCTP: [Errno 62] Protocol not supported on AIX")
+@unittest.skipIf(EMSCRIPTEN, "IPPROTO_SCTP: aborts on Emscripten")
 class SendmsgSCTPStreamTest(SendmsgStreamTests, SendrecvmsgSCTPStreamTestBase):

[emmatyping]

I see you've opened #30538 so I'll remove this change.

[tiran]

#30538 does not work ... it's still running the decorator and crashing node.js

[tiran]

Meh! The ugly hacks are piling up. Maybe it's easier to not use ac_cv_pthread and to add -pthread to CFLAGS or CFLAGS_NODIST after all?

[emmatyping]

I think the important bits of this ended up in #30552 so this can be closed.