C++: Add support for the spaceship operator

Author: Matthew Gretton-Dann

cpp/ql/src/semmle/code/cpp/exprs/Expr.qll

@@ -1216,3 +1216,18 @@ private predicate constantTemplateLiteral(Expr e) {
   or
   constantTemplateLiteral(e.(Cast).getExpr())
 }
+
+/**
+ * A C++ three-way comparison operation, also known as the _spaceship
+ * operation_.  This is specific to C++20 and later.
+ * ```
+ * auto c = (a <=> b);
+ * ```
+ */
+class SpaceshipExpr extends BinaryOperation, @spaceshipexpr {
+  override string getCanonicalQLClass() { result = "SpaceshipExpr" }
+
+  override int getPrecedence() { result = 11 }
+
+  override string getOperator() { result = "<=>" }
+}

cpp/ql/src/semmlecode.cpp.dbscheme

@@ -1231,6 +1231,7 @@ funbind(
              | @ltexpr
              | @geexpr
              | @leexpr
+             | @spaceshipexpr
              ;
 
 @bin_bitwise_op_expr = @lshiftexpr
@@ -1636,6 +1637,7 @@ case @expr.kind of
 | 323 = @vec_fill
 | 324 = @builtinconvertvector
 | 325 = @builtincomplex
+| 326 = @spaceshipexpr
 ;
 
 new_allocated_type(