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719b2ac42e
In order to test libc++ under the "Apple System Library" configuration, we need to run the tests using DYLD_LIBRARY_PATH. This is required because libc++ gets an install_name of /usr/lib when built as a system library, which means that we must override the copy of libc++ used by the whole process. This effectively reverts 2cf2f1b, which was the wrong solution for the problem I was having. Of course, this assumes that the just-built libc++ is sufficient to replace the system library, which is not actually the case out-of-the-box. Indeed, the system library contains a few symbols that are not provided by the upstream library, leading to undefined symbols when replacing the system library by the just-built one. To solve this problem, we separately build shims that provide those missing symbols and we manually link against them when we build executables in the tests. While this is somewhat brittle, it provides a localized and unintrusive way to allow testing the Apple system configuration in an upstream environment, which has been a frequent request.
libc++ / libc++abi configuration caches
This directory contains CMake caches for the supported configurations of libc++. Some of the configurations are specific to a vendor, others are generic and not tied to any vendor.
While we won't explicitly work to break configurations not listed here, any configuration not listed here is not explicitly supported. If you use or ship libc++ under a configuration not listed here, you should work with the libc++ maintainers to make it into a supported configuration and add it here.
Similarly, adding any new configuration that's not already covered must be discussed with the libc++ maintainers as it entails a maintenance burden.