Add foreach_unique iteration construct.

Idea via Ingo Wald / IVL compiler.

tests_errors/foreach-unique-1.ispc

@@ -0,0 +1,12 @@
+// Iteration domain type in "foreach_tiled" loop must be an atomic, pointer, or enum type
+
+struct Point { float x, y; };
+
+uniform int foo(Point p) {
+    uniform int count = 0;
+    foreach_unique (pt in p)
+        ++count;
+    return count;
+}
+
+

tests_errors/foreach-unique-2.ispc

@@ -0,0 +1,8 @@
+// Can't assign to type "const uniform int32"
+
+void foo(int x) {
+    foreach_unique (u in x)
+        ++u;
+}
+
+

tests_errors/foreach-unique-3.ispc

@@ -0,0 +1,10 @@
+// Error: "break" statement is illegal outside of for/while/do loops
+
+void foo(int x) {
+    foreach_unique (u in x) {
+        if (u == 0)
+            break;
+    }
+}
+
+

tests_errors/foreach-unique-4.ispc

@@ -0,0 +1,10 @@
+// Error: "return" statement is illegal inside a "foreach" loop
+
+void foo(int x) {
+    foreach_unique (u in x) {
+        if (u == 0)
+            return;
+    }
+}
+
+