Saturation arithmetic mul and div for int8/int16/int32 and div for int64 was added

tests/pdivus_i64.ispc

@@ -0,0 +1,21 @@
+
+export uniform int width() { return programCount; }
+
+export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
+    uniform unsigned int64 a_max = 18446744073709551615, a_min = 0; // max and min unsigned int64
+    if (programIndex % 2 == 0) {
+        RET[programIndex] = saturating_div(a_min, (uniform unsigned int64) b);
+    }
+    else {
+        RET[programIndex] = saturating_div(a_max, (uniform unsigned int64) b);
+    } 
+}
+
+export void result(uniform float RET[]) {
+    if (programIndex % 2 == 0) {
+        RET[programIndex] = (uniform unsigned int64) 0;
+    }
+    else {
+        RET[programIndex] = (uniform unsigned int64) 3689348814741910323;
+    } 
+}