Extract constant cycle tests.

test/libsolidity/syntaxTests/constants/cyclic_dependency_1.sol

@@ -0,0 +1,5 @@
+contract C {
+    uint constant a = a;
+}
+// ----
+// TypeError: The value of the constant a has a cyclic dependency via a.

test/libsolidity/syntaxTests/constants/cyclic_dependency_2.sol

@@ -0,0 +1,10 @@
+contract C {
+    uint constant a = b * c;
+    uint constant b = 7;
+    uint constant c = b + uint(keccak256(d));
+    uint constant d = 2 + a;
+}
+// ----
+// TypeError: The value of the constant a has a cyclic dependency via c.
+// TypeError: The value of the constant c has a cyclic dependency via d.
+// TypeError: The value of the constant d has a cyclic dependency via a.

test/libsolidity/syntaxTests/constants/cyclic_dependency_3.sol

@@ -0,0 +1,11 @@
+contract C {
+    uint constant x = a;
+    uint constant a = b * c;
+    uint constant b = c;
+    uint constant c = b;
+}
+// ----
+// TypeError: The value of the constant x has a cyclic dependency via a.
+// TypeError: The value of the constant a has a cyclic dependency via b.
+// TypeError: The value of the constant b has a cyclic dependency via c.
+// TypeError: The value of the constant c has a cyclic dependency via b.

test/libsolidity/syntaxTests/constants/cyclic_dependency_4.sol

@@ -0,0 +1,6 @@
+contract C {
+    uint constant a = b * c;
+    uint constant b = 7;
+    uint constant c = 4 + uint(keccak256(d));
+    uint constant d = 2 + b;
+}