Adds explicit alignment information for alloca instructions in general, there's a few cases that still needs to be looked at but this should catch the majority. Fixes ticket #293 .

struct Vertex {
    uint[1] c;
}

void main() {
    uint[1] c = 0xffffffff;

    auto v = Vertex(c);

    assert(v.c[0] == 0xffffffff);  // fails in LDC
}