[nix-shell:~/dev/zig/build]$ cmake .. -DCMAKE_PREFIX_PATH=$HOME/local/llvm9-release
-- The C compiler identification is unknown
-- The CXX compiler identification is unknown
CMake Error at CMakeLists.txt:18 (project):
  The CMAKE_C_COMPILER:

    /nix/store/382vgzzm7xrkqfply7y1h3fn03hp68m5-gcc-wrapper-7.4.0/bin/gcc

  is not a full path to an existing compiler tool.

  Tell CMake where to find the compiler by setting either the environment
  variable "CC" or the CMake cache entry CMAKE_C_COMPILER to the full path to
  the compiler, or to the compiler name if it is in the PATH.


CMake Error at CMakeLists.txt:18 (project):
  The CMAKE_CXX_COMPILER:

    /nix/store/382vgzzm7xrkqfply7y1h3fn03hp68m5-gcc-wrapper-7.4.0/bin/g++

  is not a full path to an existing compiler tool.

  Tell CMake where to find the compiler by setting either the environment
  variable "CXX" or the CMake cache entry CMAKE_CXX_COMPILER to the full path
  to the compiler, or to the compiler name if it is in the PATH.


-- Configuring incomplete, errors occurred!
See also "/home/andy/dev/zig/build/CMakeFiles/CMakeOutput.log".
See also "/home/andy/dev/zig/build/CMakeFiles/CMakeError.log".