[EOSIO/eos] build target error (#5332)

You appear to be attempting to build a Hello World contract using a CMake project generated by CLion. If you used default options to generate your CMake project, you’ll need to add a great many options. First, be sure CMake is using `clang`. Then be sure it includes all of the options from the `eosiocpp` script. I would guess you are missing at least `-nostdinc -nostdlibinc`. You also need `-emit-llvm —std=c++14 —target=wasm32 -nostdlib -ffreestanding -fno-threadsafe-statics -fno-rtti -fno-exceptions`. See the `eosiocpp` script in your `eos/build/tools` directory for the required steps for building a contract that can be loaded into the chain. Heavy customization will be required to make your CLion environment work.