LLVM_PREFIX not declare


I am installing cilkplus/llvm but after 89% of installation,I encountered an error which says “/llvm/tools/clang/lib/Driver/ToolChains.cpp:1510:42: error: ‘LLVM_PREFIX’ was not declared in this scope” which is this line “std::string PrefixRelDir = std::string(LLVM_PREFIX) + “/…/gnu”;”. I look at the file but couldn’t find out the problem and Google too but problem yet not fixed. I don’t know what it means. I will be very helpful, I could get some help from here!!!

Thank you.

And I am getting these two errors too.

make[2]: *** [tools/clang/lib/Driver/CMakeFiles/clangDriver.dir/ToolChains.cpp.o] Error 1
make[1]: *** [tools/clang/lib/Driver/CMakeFiles/clangDriver.dir/all] Error 2

​please help me to fix these errors.

Thank you