raise error using zig as cross compile

[zhouhaiming]

    # nim c -f --cc:zig --zig.options.linker:"-target arm-linux-musleabihf" 
--zig.options.always:"-target arm-linux-musleabihf" hello.nim
    command line(1, 2) Error: unknown C compiler: 'zig'. Available options are: 
gcc, switch_gcc, llvm_gcc, clang, bcc, vcc, tcc, env, icl, icc, clang_cl
    
    
    Run
    
    
    # nim --version
    Nim Compiler Version 1.3.5 [Linux: amd64]
    Compiled at 2020-05-20
    Copyright (c) 2006-2020 by Andreas Rumpf
    
    git hash: 6969a468ceaab7384d7448bfd88e47a5b24c3a97
    active boot switches: -d:release
    
    
    Run
    
    
    # zig version
    0.6.0
    
    
    Run
    
    
    # cat hello.nim
    echo "Hello World"
    
    
    Run