The _testcapimodule.c file is getting too large to work with effectively.
Vectorcall tests aren't the biggest issue -- it's just an area I want to work
on next, so I started there.
It does make it clear that MethodDescriptor2 is related to testing vectorcall,
which wasn't clear before (the /* Test PEP 590 */ section had an ambiguous end).

This PR lays out a general structure of how tests can be split up,
with more splitting to come later if the structure is OK.

The `_testcapimodule.c` file is getting too large to work with effectively.
This PR lays out a general structure of how tests can be split up, with more splitting to come later if the structure is OK.

Vectorcall tests aren't the biggest issue -- it's just an area I want to work on next, so I'm starting here.
An issue specific to vectorcall tests is that it wasn't clear that e.g. `MethodDescriptor2` is related to testing vectorcall: the `/* Test PEP 590 */` section had an ambiguous end. Separate file should make things like this much clearer.
OTOH, for some pieces it might not be clear where they should be -- I left `meth_fastcall` with tests of the other calling conventions. IMO, even with the ambiguity it's still worth it to split the huge file up.

I'm not sure about the buildsystem changes, hopefully CI will tell me what's wrong.

@vstinner, @markshannon: Do you think this is a good idea?

Automerge-Triggered-By: GH:encukou

- header files are located in $(srcdir)
- dependencies must not list C files that are also in a makesetup Setup
  file

- header files are located in $(srcdir)
- dependencies must not list C files that are also in a makesetup Setup file
- generate SRCDIRS for OOT builds

This removes the unused negative_dictoffset function:
the type this function would create is available as
    _testcapi.HeapCTypeWithNegativeDict

)

* main: (8272 commits)
  Update Windows readme.txt to clarify Visual Studio required versions (pythonGH-99522)
  pythongh-99460 Emscripten trampolines on optimized METH_O and METH_NOARGS code paths (python#99461)
  pythongh-92647: [Enum] use final status to determine lookup or create (pythonGH-99500)
  pythongh-81057: Move Globals in Core Code to _PyRuntimeState (pythongh-99496)
  Post 3.12.0a2
  pythongh-99300: Use Py_NewRef() in Python/Python-ast.c (python#99499)
  pythongh-93649: Split pytime and datetime tests from _testcapimodule.c (python#99494)
  pythongh-99370: fix test_zippath_from_non_installed_posix (pythonGH-99483)
  pythonGH-99205: remove `_static` field from `PyThreadState` and `PyInterpreterState` (pythonGH-99385)
  pythongh-81057: Move the Remaining Import State Globals to _PyRuntimeState (pythongh-99488)
  pythongh-87604: Avoid publishing list of active per-interpreter audit hooks via the gc module (pythonGH-99373)
  pythongh-93649: Split getargs tests from _testcapimodule.c (python#99346)
  pythongh-81057: Move Global Variables Holding Objects to _PyRuntimeState. (pythongh-99487)
  pythonGH-98219: reduce sleep time in `asyncio` subprocess test (python#99464)
  pythonGH-99388: add `loop_factory` parameter to `asyncio.run` (python#99462)
  pythongh-99300: Use Py_NewRef() in PC/ directory (python#99479)
  pythongh-99300: Use Py_NewRef() in Doc/ directory  (python#99480)
  pythongh-99300: Use Py_NewRef() in Modules/ directory (python#99473)
  pythongh-99300: Use Py_NewRef() in Modules/ directory (python#99469)
  pythongh-99370: Calculate zip path from prefix when in a venv (pythonGH-99371)
  ...

…9517)

Automerge-Triggered-By: GH:erlend-aasland

* origin/main: (1306 commits)
  Correct CVE-2020-10735 documentation (python#100306)
  pythongh-100272: Fix JSON serialization of OrderedDict (pythonGH-100273)
  pythongh-93649: Split tracemalloc tests from _testcapimodule.c (python#99551)
  Docs: Use `PY_VERSION_HEX` for version comparison (python#100179)
  pythongh-97909: Fix markup for `PyMethodDef` members (python#100089)
  pythongh-99240: Reset pointer to NULL when the pointed memory is freed in argument parsing (python#99890)
  pythongh-99240: Reset pointer to NULL when the pointed memory is freed in argument parsing (python#99890)
  pythonGH-98831: Add DECREF_INPUTS(), expanding to DECREF() each stack input (python#100205)
  pythongh-78707: deprecate passing >1 argument to `PurePath.[is_]relative_to()` (pythonGH-94469)
  pythongh-99540: Constant hash for _PyNone_Type to aid reproducibility (pythonGH-99541)
  pythongh-100039: enhance __signature__ to work with str and callables (pythonGH-100168)
  pythongh-99830: asyncio: Document returns of remove_{reader,writer} (python#100302)
  "Compound statement" docs: Fix with-statement step indexing (python#100286)
  pythonGH-90043: Handle NaNs in COMPARE_OP_FLOAT_JUMP (pythonGH-100278)
  Improve stats presentation for calls. (pythonGH-100274)
  Better stats for `LOAD_ATTR` and `STORE_ATTR` (pythonGH-100295)
  pythongh-81057: Move the Cached Parser Dummy Name to _PyRuntimeState (python#100277)
  Document that zipfile's pwd parameter is a `bytes` object (python#100209)
  pythongh-99767: mark `PyTypeObject.tp_watched` as internal use only in table (python#100271)
  Fix typo in introduction.rst (python#100266)
  ...

* main:
  pythongh-89727: Fix os.walk RecursionError on deep trees (python#99803)
  Docs: Don't upload CI artifacts (python#100330)
  pythongh-94912: Added marker for non-standard coroutine function detection (python#99247)
  Correct CVE-2020-10735 documentation (python#100306)
  pythongh-100272: Fix JSON serialization of OrderedDict (pythonGH-100273)
  pythongh-93649: Split tracemalloc tests from _testcapimodule.c (python#99551)
  Docs: Use `PY_VERSION_HEX` for version comparison (python#100179)
  pythongh-97909: Fix markup for `PyMethodDef` members (python#100089)
  pythongh-99240: Reset pointer to NULL when the pointed memory is freed in argument parsing (python#99890)
  pythongh-99240: Reset pointer to NULL when the pointed memory is freed in argument parsing (python#99890)
  pythonGH-98831: Add DECREF_INPUTS(), expanding to DECREF() each stack input (python#100205)
  pythongh-78707: deprecate passing >1 argument to `PurePath.[is_]relative_to()` (pythonGH-94469)