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/test_aux_runtime.pass.cc

@@ -0,0 +1,62 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 "third_party/libcxx/typeinfo"
+
+//  Test taken from 5.2.8.2
+//  When typeid is applied to a glvalue expression whose type is a polymorphic
+//  class type, (10.3), the result refers to a std::type_info object
+//  representing the type of the most derived object (1.8) (that is, the
+//  dynamic type) to which the glvalue refers. If the glvalue expression is
+//  obtained by applying the unary * operator to a pointer(68) and the pointer
+//  is a null pointer value (4.10), the typeid expression throws the
+//  std::bad_typeid exception (18.7.3).
+//
+//  68) If p is an expression of pointer type, then *p, (*p), *(p),
+//      ((*p)), *((p)), and so on all meet this requirement.
+bool bad_typeid_test () {
+    class A { virtual void f() {}};
+    class B { virtual void g() {}};
+
+    B *bp = NULL;
+    try {bool b = typeid(*bp) == typeid (A); ((void)b); }
+    catch ( const std::bad_typeid &) { return true; }
+    return false;
+}
+
+
+//  The value of a failed cast to pointer type is the null pointer value of
+//  the required result type. A failed cast to reference type throws
+//  std::bad_cast (18.7.2).
+bool bad_cast_test () {
+    class A { virtual void f() {}};
+    class B { virtual void g() {}};
+    class D : public virtual A, private B {};
+
+    D d;
+    B *bp = (B*)&d;     // cast needed to break protection
+    try { D &dr = dynamic_cast<D&> (*bp); ((void)dr); }
+    catch ( const std::bad_cast & ) { return true; }
+    return false;
+}
+
+int main ( ) {
+    int ret_val = 0;
+
+    if ( !bad_typeid_test ()) {
+        ret_val = 1;
+    }
+
+    if ( !bad_cast_test ()) {
+        ret_val = 2;
+    }
+
+    return ret_val;
+}