/*
   * Define the architecture of the pool.
   *
   * Only Solvables with a compatible architecture will be considered
   * during solving.
   *
   * Setting the architecture to "i686" is a good choice for most 32bit
   * systems, 64bit systems most probably need "x86_64"
   * Attn: There is no getter function for the architecture since
   * setting an architecture is converted to a list of 'compatible'
   * architectures internally. E.g. i686 is actually
   * i686,i586,i486,i386,noach. The solver will always choose the
   * 'best' architecture from this list.
   *
   * call-seq:
   *  pool.arch = "i686"
   *
   */
  void set_arch( const char *arch )