[Sema][NFC] Add tests for builtin spaceship operator.

In preparation for D112453.

clang/test/CXX/over/over.built/ast-20.cpp

@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -std=c++20 -ast-dump %s -ast-dump-filter Test | FileCheck %s
+
+namespace std {
+  struct strong_ordering {
+    int n;
+    constexpr operator int() const { return n; }
+    static const strong_ordering less, equal, greater;
+  };
+  constexpr strong_ordering strong_ordering::less{-1},
+      strong_ordering::equal{0}, strong_ordering::greater{1};
+}
+
+template <typename T, typename U>
+auto Test(T* pt, U* pu) {
+  // CHECK: BinaryOperator {{.*}} '<dependent type>' '<=>'
+  // CHECK-NEXT: DeclRefExpr {{.*}} 'T *' lvalue ParmVar {{.*}} 'pt' 'T *'
+  // CHECK-NEXT: DeclRefExpr {{.*}} 'U *' lvalue ParmVar {{.*}} 'pu' 'U *'
+  (void)(pt <=> pu);
+
+}
+
+

clang/test/CXX/over/over.built/spaceship.cpp

@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -std=c++20 -verify %s -Wno-tautological-compare
+
+namespace std {
+  struct strong_ordering {
+    int n;
+    constexpr operator int() const { return n; }
+    static const strong_ordering less, equal, greater;
+  };
+  constexpr strong_ordering strong_ordering::less{-1},
+      strong_ordering::equal{0}, strong_ordering::greater{1};
+}
+
+template <typename T>
+void f(int i, int* pi, T* pt, T t) {
+  (void)(i <=> i);
+  (void)(i <=> pi); // expected-error {{comparison between pointer and integer}}
+  (void)(i <=> pt);
+  (void)(pi <=> pt);
+  (void)(pi <=> t);
+}
+