[svn r374] Move label target basic block from AST to IRFunction. This is a first step to allowing labels to be emitted multiple times. (for instance within finally blocks)

module c;

void main()
{
    ushort a = 0xFFF0;
    ushort b = 0x0FFF;
    auto t = a & b;
    a &= b;
    assert(t == a);
}