Constbits: Repeat evaluation of Phi operands, if necessary.
Constbits: Repeat evaluation of Phi operands, if necessary.

This fixes opt/fehler308.c.

jonashaag/libfirm,jonashaag/libfirm,jonashaag/libfirm,MatzeB/libfirm,MatzeB/libfirm,libfirm/libfirm,MatzeB/libfirm,libfirm/libfirm,libfirm/libfirm,jonashaag/libfirm,jonashaag/libfirm,libfirm/libfirm,MatzeB/libfirm,MatzeB/libfirm,libfirm/libfirm,jonashaag/libfirm,MatzeB/libfirm,jonashaag/libfirm,MatzeB/libfirm