Add reduce_equal() function to standard library.

tests/reduce-equal-12.ispc

@@ -0,0 +1,18 @@
+
+export uniform int width() { return programCount; }
+
+export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
+    int a = 10 + aFOO[programIndex/2];
+    RET[programIndex] = 1;
+    uniform int sameVal;
+    uniform bool re;
+    if (a <= 11) {
+        re = reduce_equal(a, sameVal);
+//CO        print("% % %\n", re, sameVal, a);
+    }
+    RET[programIndex] = ((int)re << 8) + sameVal;
+}
+
+export void result(uniform float RET[]) {
+    RET[programIndex] = 267;
+}