Comment 14 for bug 641397

http://gcc.gnu.org/ml/gcc-patches/2012-11/msg00952.html
Will improve the testcase at the tree level for little-endian:
  _4 = (unsigned char) a_3(D);
  _5 = (<unnamed-unsigned:5>) _4;
  BIT_FIELD_REF <D.1727, 10, 0> = 65;
  D.1727.c = 3;
  D.1727.d = _5;
  return D.1727;

And will fix it on big-endian:
  D.1354_2 = (unsigned char) a_1(D);
  D.1355_3 = (<unnamed-unsigned:5>) D.1354_2;
  BIT_FIELD_REF <D.1356, 15, 0> = 1091;
  D.1356.d = D.1355_3;