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/array-assignment-varying-control.ispc

@@ -11,8 +11,11 @@ void f(reference uniform Foo foo[], float a) {
 
 export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
     float a = aFOO[programIndex];
-    float f[40] = a;
-    float g[40] = b;
+    float f[40], g[40];
+    for (uniform int i = 0; i < 40; ++i) {
+        f[i] = a;
+        g[i] = b;
+    }
     if (a < 2)
         f = g;
     RET[programIndex] = f[a];