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/cxa_bad_cast.pass.cc

@@ -0,0 +1,57 @@
+//===----------------------------------------------------------------------===//
+//
+// 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: c++03
+
+#include "third_party/libcxxabi/include/cxxabi.h"
+#include "third_party/libcxx/cassert"
+#include "libc/isystem/stdlib.h"
+#include "third_party/libcxx/exception"
+#include "third_party/libcxx/typeinfo"
+
+#include "third_party/libcxxabi/libcxx/test/support/test_macros.hh"
+
+class Base {
+  virtual void foo() {};
+};
+
+class Derived : public Base {};
+
+Derived &test_bad_cast(Base& b) {
+  return dynamic_cast<Derived&>(b);
+}
+
+Base gB;
+
+void my_terminate() { exit(0); }
+
+int main ()
+{
+    // swap-out the terminate handler
+    void (*default_handler)() = std::get_terminate();
+    std::set_terminate(my_terminate);
+
+#ifndef TEST_HAS_NO_EXCEPTIONS
+    try {
+#endif
+        Derived &d = test_bad_cast(gB);
+        assert(false);
+        ((void)d);
+#ifndef TEST_HAS_NO_EXCEPTIONS
+    } catch (std::bad_cast const&) {
+        // success
+        return 0;
+    } catch (...) {
+        assert(false);
+    }
+#endif
+
+    // failure, restore the default terminate handler and fire
+    std::set_terminate(default_handler);
+    std::terminate();
+}