[runtimes] Removed support for LLVM_ENABLE_PROJECTS in libcxx, libcxxabi and libunwind


Building libc++, libc++abi and libunwind using LLVM_ENABLE_PROJECTS has been deprecated since October 2021. After working with various users of the runtimes build to migrate them to LLVM_ENABLE_RUNTIMES, I just checked-in ⚙ D132480 [llvm] Remove libcxx, libcxxabi and libunwind from supported LLVM_ENABLE_PROJECTS again, which removes support for using libcxx, libcxxabi and libunwind from LLVM_ENABLE_PROJECTS.

This is a breaking change for anyone building with these projects inside LLVM_ENABLE_PROJECTS. Instead, please move to LLVM_ENABLE_RUNTIMES as documented here and contact us if you encounter any issues with that.

Louis & the libc++ contributors