MNT: Remove compression shared libraries from global options

Paul McCarthyrequested to merge
mnt/zlib-ng into master

These flags should be able to be isolated in the znzlib project. A couple of other changes:

  • Removed -D_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR from compiler flags - this was added to be able to use old versions of libxml++ which used std::auto_ptr, and should no longer be necessary.
  • Fix the default -arch flag on macOS (only relevant when using an alternate compiler toolchain).

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