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

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

tests/array-mixed-unif-vary-indexing.ispc

@@ -10,6 +10,7 @@ export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
         for (uniform int j = 0; j < 47; ++j)
             x[i][j] = 2+b-5;
 
+    a = min(a,46);
     x[a][b-1] = 0;
     RET[programIndex] = x[2][a];
 }