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

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

tests/array-multidim-gather-scatter.ispc

@@ -11,7 +11,7 @@ export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
 
     uniform int index[4] = { 0, 1, 2, 4 };
     float v = index[programIndex & 0x3];
-    x[a][v] = 0;
+    x[min(a,39)][v] = 0;
     RET[programIndex] = x[v+1][v];
 }