Add #const field flag

core/odin/ast/ast.odin

@@ -585,6 +585,7 @@ Field_Flag :: enum {
 	No_Alias,
 	C_Vararg,
 	Auto_Cast,
+	Const,
 	Any_Int,
 	Subtype,
 	By_Ptr,
@@ -604,6 +605,7 @@ field_flag_strings := [Field_Flag]string{
 	.No_Alias           = "#no_alias",
 	.C_Vararg           = "#c_vararg",
 	.Auto_Cast          = "auto_cast",
+	.Const              = "#const",
 	.Any_Int            = "#any_int",
 	.Subtype            = "#subtype",
 	.By_Ptr             = "#by_ptr",
@@ -617,6 +619,7 @@ field_flag_strings := [Field_Flag]string{
 field_hash_flag_strings := []struct{key: string, flag: Field_Flag}{
 	{"no_alias", .No_Alias},
 	{"c_vararg", .C_Vararg},
+	{"const",    .Const},
 	{"any_int",  .Any_Int},
 	{"subtype",  .Subtype},
 	{"by_ptr",   .By_Ptr},
@@ -637,6 +640,7 @@ Field_Flags_Signature :: Field_Flags{
 	.Using,
 	.No_Alias,
 	.C_Vararg,
+	.Const,
 	.Auto_Cast,
 	.Any_Int,
 	.By_Ptr,