It is no longer legal to initialize arrays and structs with single

scalar values (that ispc used to smear across the array/struct
elements).  Now, initializers in variable declarations must be
{ }-delimited lists, with one element per struct member or array
element, respectively.

There were a few problems with the previous implementation of the
functionality to initialize from scalars.  First, the expression
would be evaluated once per value initialized, so if it had side-effects,
the wrong thing would happen.  Next, for large multidimensional arrays,
the generated code would be a long series of move instructions, rather
than loops (and this in turn made LLVM take a long time.)

While both of these problems are fixable, it's a non-trivial
amount of re-plumbing for a questionable feature anyway.

Fixes issue #50.

tests/nested-structs.ispc

@@ -13,7 +13,10 @@ struct Bar {
 
 export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
     float a = aFOO[programIndex];
-    uniform Bar bar = 2.;
+    uniform Bar bar;
+    for (uniform int i = 0; i < 6; ++i)
+        for (uniform int j = 0; j < 6; ++j)
+            bar.foo[i].f[j] = 2.;
     RET[programIndex] = bar.foo[b].f[b];
 }