apple
build: adopt current best practices for installation
Add the *_INSTALL_NESTED_SUBDIR option and use -print-target-info to compute the install locations. This reduces the number of times we need to invoke the compiler and compute these values.
This is replicating what has been done with swift-testing, swift-corelibs-xctest, and is in the process of being applied to swift-corelibs-libdispatch as well.
The change itself looks ok to me now - thanks for the explanations, but since this repo can't test CMake changes can you build a Linux + Windows toolchain via a cross-repo PR so that we can compare the toolchains and make sure that things still build and that they end up in the right places?
Seems that the Linux toolchain build did uncover something. Will take a look once I clear up some more of the Windows patches.