Allow static, non-framework iOS builds

Feature or enhancement

Proposal:

configure refuses any iOS build that is not a framework build, in both the explicit and the default path:

configure.ac:582   iOS) AC_MSG_ERROR([iOS builds must use --enable-framework]) ;;   # --disable-framework
configure.ac:692   iOS) AC_MSG_ERROR([iOS builds must use --enable-framework]) ;;   # no framework option given

The requirement is sound for a shared Python: an iOS app can only load a signed framework, never a bare dylib, so a dynamically loaded libpython has to be packaged as one. It does not hold for a static one. A --disable-shared build produces libpython3.x.a, which is linked into the app binary and loads nothing at runtime, so there is no framework to sign, package or load — but configure rejects that configuration before it can be attempted.

This matters for embedders, which link libpython statically into a single signed executable. Today they have to either patch configure locally or give up sys.platform == "ios" and cross-build as Darwin, which misreports the platform to the stdlib.

Two other places assume the framework exists whenever ac_sys_system is iOS:

configure.ac:3838  LINKFORSHARED="… $(PYTHONFRAMEWORKDIR)/$(PYTHONFRAMEWORK)"
configure.ac:6767  MODULE_DEPS_SHARED="… $(PYTHONFRAMEWORKDIR)/$(PYTHONFRAMEWORK)"

The Darwin arm immediately above the first one already guards the identical append with if test "$enable_framework"; the iOS arm does it unconditionally.

Suggested shape, keeping the change conservative:

• refuse only the combination that genuinely cannot work — a shared build with no framework — checked once PY_ENABLE_SHARED is known;
• gate the two framework appends on enable_framework, matching the Darwin arm;
• leave the default path (no framework option at all) erroring, so a non-framework build stays an explicit opt-in, with the message naming --disable-framework.

I have this working against main and will open a PR. Verified locally on macOS/arm64:

• --host=arm64-apple-ios12.0 --disable-shared --disable-framework configures and make libpython3.16.a succeeds, producing an arm64 archive with LC_BUILD_VERSION platform 2, minos 12.0;
• --disable-framework --enable-shared is rejected with the new message;
• no framework option is still rejected;
• --enable-framework produces a byte-identical Makefile and pyconfig.h to unpatched main, so the supported framework build is unaffected.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-156110

從 configure.ac 的第 582、692、3838 和 6767 行開始，然後將 iOS 的處理與附近顯示的 Darwin arm 處理進行比較。驗證 issue 中所述的 shared 和 static configure 組合，確認 framework 建置保持不變，並檢查 static 建置是否成功產生 libpython3.16.a。