Fix ICE when a constant variable declaration forward references a struct

test/libsolidity/syntaxTests/constantEvaluator/type_reference.sol

@@ -1,3 +1,4 @@
 int[L] constant L = 6;
 // ----
 // TypeError 5462: (4-5): Invalid array length, expected integer literal or constant expression.
+// TypeError 9259: (0-21): Only constants of value type and byte arrays are implemented.

test/libsolidity/syntaxTests/constantEvaluator/type_reference_in_contract.sol

@@ -3,3 +3,4 @@ contract C {
 }
 // ----
 // TypeError 5462: (21-22): Invalid array length, expected integer literal or constant expression.
+// TypeError 9259: (17-38): Only constants of value type and byte arrays are implemented.

test/libsolidity/syntaxTests/constants/mapping_constant.sol

@@ -1,3 +1,3 @@
 mapping(uint => uint) constant b = b;
 // ----
-// DeclarationError 3530: (0-36): The type contains a (nested) mapping and therefore cannot be a constant.
+// TypeError 9259: (0-36): Only constants of value type and byte arrays are implemented.

test/libsolidity/syntaxTests/constants/struct_constant.sol

@@ -1,4 +1,4 @@
 struct S { uint x; }
 S constant s;
 // ----
-// TypeError 9259: (21-33): Constants of non-value type not yet implemented.
+// TypeError 9259: (21-33): Only constants of value type and byte arrays are implemented.

test/libsolidity/syntaxTests/iceRegressionTests/const_struct_with_mapping.sol

@@ -5,4 +5,4 @@ contract C {
     S public constant e = 0x1212121212121212121212121212121212121212;
 }
 // ----
-// DeclarationError 3530: (71-135): The type contains a (nested) mapping and therefore cannot be a constant.
+// TypeError 9259: (71-135): Only constants of value type and byte arrays are implemented.

test/libsolidity/syntaxTests/nameAndTypeResolution/105_constant_input_parameter.sol

@@ -3,3 +3,4 @@ contract test {
 }
 // ----
 // DeclarationError 1788: (31-55): The "constant" keyword can only be used for state variables or variables at file level.
+// TypeError 9259: (31-55): Only constants of value type and byte arrays are implemented.

test/libsolidity/syntaxTests/nameAndTypeResolution/171_assignment_to_const_array_vars.sol

@@ -2,4 +2,4 @@ contract C {
     uint[3] constant x = [uint(1), 2, 3];
 }
 // ----
-// TypeError 9259: (17-53): Constants of non-value type not yet implemented.
+// TypeError 9259: (17-53): Only constants of value type and byte arrays are implemented.

test/libsolidity/syntaxTests/nameAndTypeResolution/173_constant_struct.sol

@@ -3,4 +3,4 @@ contract C {
     S constant x = S(5, new uint[](4));
 }
 // ----
-// TypeError 9259: (52-86): Constants of non-value type not yet implemented.
+// TypeError 9259: (52-86): Only constants of value type and byte arrays are implemented.

test/libsolidity/syntaxTests/nameAndTypeResolution/constant_forward_reference_struct.sol

@@ -0,0 +1,4 @@
+S constant x;
+struct S { int y; }
+// ----
+// TypeError 9259: (0-12): Only constants of value type and byte arrays are implemented.

test/libsolidity/syntaxTests/nameAndTypeResolution/constant_mapping.sol

@@ -2,4 +2,4 @@ contract C {
     mapping(uint => uint) constant x;
 }
 // ----
-// DeclarationError 3530: (17-49): The type contains a (nested) mapping and therefore cannot be a constant.
+// TypeError 9259: (17-49): Only constants of value type and byte arrays are implemented.

test/libsolidity/syntaxTests/nameAndTypeResolution/constant_nested_mapping.sol

@@ -5,4 +5,4 @@ contract C {
     S public constant c;
 }
 // ----
-// DeclarationError 3530: (71-90): The type contains a (nested) mapping and therefore cannot be a constant.
+// TypeError 9259: (71-90): Only constants of value type and byte arrays are implemented.

test/libsolidity/syntaxTests/parsing/location_specifiers_for_params.sol

@@ -3,3 +3,4 @@ contract Foo {
 }
 // ----
 // DeclarationError 1788: (30-55): The "constant" keyword can only be used for state variables or variables at file level.
+// TypeError 9259: (30-55): Only constants of value type and byte arrays are implemented.