public enum class Library(public val libName: String) {
  STDIO("stdio")
  THREAD("pthread") //this could be extended to include different libraries based on platform
  MATH("math")
  STRING("string")
}

fun Runtime.C.includes(varags includes: Library) {
  //probably better to fold, but whatever =p
  var sum: String = ""
  includes.forEach { lib ->
    sum += "#ifndef __INCLUDED_${lib.libName.toUpperCase}"
    sum += "#include <${lib.libName}>"
    sum += "#endif"
  }
  //do whatever you need to do to get sum added to the top of the includes
}

used like:
Runtime.C.includes(Library.STDIO, Library.MATH)