You can provide the path to this library manually, e.g. my running ccmake instead of cmake. It should be found in a path similar to this one depending on the XCode version you've installed:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/11.0.0/lib/darwin/libclang_rt.osx.a