Fix a number of tests to work correctly with 32/64-wide targets.

Still to be reviewed/fixed: tests/test-*, tests/[cfrs]*

tests/array-struct-gather.ispc

@@ -4,14 +4,14 @@ export uniform int width() { return programCount; }
 
 
 struct Foo {
-    uniform float x[17];
+    uniform float x[programCount+1];
 };
 
 export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
     float a = aFOO[programIndex];
     uniform Foo foo;
     uniform int i;
-    for (i = 0; i < 17; ++i)
+    for (i = 0; i < programCount+1; ++i)
         foo.x[i] = i;
 
     if ((int)a & 1)