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/unwind_02.pass.cc

@@ -0,0 +1,105 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+// REQUIRES: c++03 || c++11 || c++14
+
+#include "libc/isystem/assert.h"
+
+#if defined(__GNUC__)
+#pragma GCC diagnostic ignored "-Wunreachable-code"
+#pragma GCC diagnostic ignored "-Wdeprecated" // dynamic exception specifications are deprecated
+#endif
+
+struct A
+{
+    static int count;
+    int id_;
+    A() : id_(++count) {}
+    ~A() {assert(id_ == count--);}
+
+private:
+    A(const A&);
+    A& operator=(const A&);
+};
+
+int A::count = 0;
+
+struct B
+{
+    static int count;
+    int id_;
+    B() : id_(++count) {}
+    ~B() {assert(id_ == count--);}
+
+private:
+    B(const B&);
+    B& operator=(const B&);
+};
+
+int B::count = 0;
+
+struct C
+{
+    static int count;
+    int id_;
+    C() : id_(++count) {}
+    ~C() {assert(id_ == count--);}
+
+private:
+    C(const C&);
+    C& operator=(const C&);
+};
+
+int C::count = 0;
+
+void f2()
+{
+    C c;
+    A a;
+    throw 55;
+    B b;
+}
+
+void f1() throw (long, char, int, double)
+{
+    A a;
+    B b;
+    f2();
+    C c;
+}
+
+int main(int, char**)
+{
+    try
+    {
+        f1();
+        assert(false);
+    }
+    catch (int* i)
+    {
+        assert(false);
+    }
+    catch (long i)
+    {
+        assert(false);
+    }
+    catch (int i)
+    {
+        assert(i == 55);
+    }
+    catch (...)
+    {
+        assert(false);
+    }
+    assert(A::count == 0);
+    assert(B::count == 0);
+    assert(C::count == 0);
+
+    return 0;
+}