third_party/libcxxabi: Add test suite (#1076)

Added the `libcxxabi` test suite as found in LLVM 17.0.6.

Some tests that do not apply to the current configuration of
comsopolitan are not added. These include:
- `backtrace_test`, `forced_unwind*`: Use unwind function unsupported in
SjLj mode.
- `noexception*`: Designed to test `libcxxabi` in no exceptions mode.

Some tests are added but not enabled due to bugs specific to GCC or
cosmopolitan. These are clearly indicated in the `BUILD.mk` file.

third_party/libcxxabi/test/catch_class_01.pass.cc

@@ -0,0 +1,61 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: no-exceptions
+
+#include <exception>
+#include <stdlib.h>
+#include <assert.h>
+
+struct A
+{
+    static int count;
+    int id_;
+    explicit A(int id) : id_(id) {count++;}
+    A(const A& a) : id_(a.id_) {count++;}
+    ~A() {count--;}
+};
+
+int A::count = 0;
+
+void f1()
+{
+    throw A(3);
+}
+
+void f2()
+{
+    try
+    {
+        assert(A::count == 0);
+        f1();
+    }
+    catch (A a)
+    {
+        assert(A::count != 0);
+        assert(a.id_ == 3);
+        throw;
+    }
+}
+
+int main(int, char**)
+{
+    try
+    {
+        f2();
+        assert(false);
+    }
+    catch (const A& a)
+    {
+        assert(A::count != 0);
+        assert(a.id_ == 3);
+    }
+    assert(A::count == 0);
+
+    return 0;
+}