Investigate necessity of HAVE_DYLD_SHARED_CACHE_CONTAINS_PATH on macOS 11

[indygreg]

According to indygreg/PyOxidizer#373 (comment) the HAVE_DYLD_SHARED_CACHE_CONTAINS_PATH feature is required on macOS 11 for things to be happy.

I had unconditionally disabled that feature flag thinking it was an optional feature.

We should probably only conditionally disable on target SDK < 11.0.

But according to @ronaldoussoren it might be required to use ctypes when running on macOS 11?! If so, then the current builds are busted, as Python 3.8 uses the 10.15 SDK and 3.9 - while using the 11.0 SDK - has the feature disabled.

[indygreg]

I may have spoken too soon: our build only disables this feature on the host CPython builds when cross-compiling. Apparently to workaround some build-time bug. But this shouldn't impact the target builds we distribute.