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On systems with glibc, clock_gettime() was moved from librt to libc in version 2.17, in which case the current librt detection attempt would always fail. Look for shm_open instead, like other parts of the tree also do when looking for librt. Co-authored-by: Raphael Kubo da Costa <kubo@igalia.com>
See docs/CMake.html for instructions on how to build LLVM with CMake.