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/inherited_exception.pass.cc

@@ -0,0 +1,173 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This test case checks specifically the cases under C++ ABI 15.3.1, and 15.3.2
+//
+//  C++ ABI 15.3:
+//  A handler is a match for an exception object of type E if
+//  >  *  The handler is of type cv T or cv T& and E and T are the same type   <
+//  >     (ignoring the top-level cv-qualifiers), or                           <
+//  >  *  the handler is of type cv T or cv T& and T is an unambiguous base    <
+//  >     class of E, or                                                       <
+//     *  the handler is of type cv1 T* cv2 and E is a pointer type that can
+//        be converted to the type of the handler by either or both of
+//          o  a standard pointer conversion (4.10 [conv.ptr]) not involving
+//             conversions to private or protected or ambiguous classes
+//          o  a qualification conversion
+//     *  the handler is a pointer or pointer to member type and E is
+//        std::nullptr_t
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: no-exceptions
+
+// Compilers emit warnings about exceptions of type 'Child' being caught by
+// an earlier handler of type 'Base'. Congrats, you've just diagnosed the
+// behavior under test.
+// ADDITIONAL_COMPILE_FLAGS: -Wno-exceptions
+
+#include "libc/isystem/assert.h"
+
+struct Base {
+  int b1;
+};
+
+struct Base2 {
+  int b2;
+};
+
+struct Child : public Base, public Base2 {
+  int c;
+};
+
+void f1() {
+  Child child;
+  child.b1 = 10;
+  child.b2 = 11;
+  child.c = 12;
+  throw child;
+}
+
+void f2() {
+  Child child;
+  child.b1 = 10;
+  child.b2 = 11;
+  child.c = 12;
+  throw static_cast<Base2&>(child);
+}
+
+void f3() {
+  static Child child;
+  child.b1 = 10;
+  child.b2 = 11;
+  child.c = 12;
+  throw static_cast<Base2*>(&child);
+}
+
+int main(int, char**)
+{
+    try
+    {
+        f1();
+        assert(false);
+    }
+    catch (const Child& c)
+    {
+        assert(true);
+    }
+    catch (const Base& b)
+    {
+        assert(false);
+    }
+    catch (...)
+    {
+        assert(false);
+    }
+
+    try
+    {
+        f1();
+        assert(false);
+    }
+    catch (const Base& c)
+    {
+        assert(true);
+    }
+    catch (const Child& b)
+    {
+        assert(false);
+    }
+    catch (...)
+    {
+        assert(false);
+    }
+
+    try
+    {
+        f1();
+        assert(false);
+    }
+    catch (const Base2& c)
+    {
+        assert(true);
+    }
+    catch (const Child& b)
+    {
+        assert(false);
+    }
+    catch (...)
+    {
+        assert(false);
+    }
+
+    try
+    {
+        f2();
+        assert(false);
+    }
+    catch (const Child& c)
+    {
+        assert(false);
+    }
+    catch (const Base& b)
+    {
+        assert(false);
+    }
+    catch (const Base2& b)
+    {
+        assert(true);
+    }
+    catch (...)
+    {
+        assert(false);
+    }
+
+    try
+    {
+        f3();
+        assert(false);
+    }
+    catch (const Base* c)
+    {
+        assert(false);
+    }
+    catch (const Child* b)
+    {
+        assert(false);
+    }
+    catch (const Base2* c)
+    {
+        assert(true);
+    }
+    catch (...)
+    {
+        assert(false);
+    }
+
+    return 0;
+}