Update run_tests and examples makefile for scalar target.

Fixed a number of tests that didn't handle the programCount == 1
case correctly.

tests/test-128.ispc

@@ -4,9 +4,9 @@ export uniform int width() { return programCount; }
 
 export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
     float a = aFOO[programIndex];
-    RET[programIndex] = extract(a, 1);
+    RET[programIndex] = extract(a, min(1, programCount-1));
 }
 
 export void result(uniform float RET[]) {
-    RET[programIndex] = 2.;
+    RET[programIndex] = (programCount == 1) ? 1 : 2.;
 }