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/unittest_demangle.pass.cc

@@ -0,0 +1,89 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+// ADDITIONAL_COMPILE_FLAGS: -Wno-unused-function
+
+#include "third_party/libcxx/cassert"
+#include "third_party/libcxx/utility"
+
+#include "third_party/libcxxabi/demangle/ItaniumDemangle.h"
+
+void testPODSmallVector() {
+  { // {push/pop}_back
+    itanium_demangle::PODSmallVector<int, 1> PSV;
+    PSV.push_back(0);
+    PSV.push_back(1);
+    PSV.push_back(2);
+    PSV.push_back(3);
+    for (int i = 0; i < 4; ++i)
+      assert(PSV[i] == i);
+    PSV.pop_back();
+    for (int i = 0; i < 3; ++i)
+      assert(PSV[i] == i);
+    PSV.pop_back();
+    PSV.pop_back();
+    assert(!PSV.empty() && PSV.size() == 1);
+    PSV.pop_back();
+    assert(PSV.empty() && PSV.size() == 0);
+  }
+
+  {
+    itanium_demangle::PODSmallVector<int, 1> PSV1;
+    PSV1.push_back(1);
+    PSV1.push_back(2);
+    PSV1.push_back(3);
+
+    itanium_demangle::PODSmallVector<int, 1> PSV2;
+    std::swap(PSV1, PSV2);
+    assert(PSV1.size() == 0);
+    assert(PSV2.size() == 3);
+    int i = 1;
+    for (int x : PSV2) {
+      assert(x == i);
+      ++i;
+    }
+    assert(i == 4);
+    std::swap(PSV1, PSV2);
+    assert(PSV1.size() == 3);
+    assert(PSV2.size() == 0);
+    i = 1;
+    for (int x : PSV1) {
+      assert(x == i);
+      ++i;
+    }
+    assert(i == 4);
+  }
+
+  {
+    itanium_demangle::PODSmallVector<int, 10> PSV1;
+    itanium_demangle::PODSmallVector<int, 10> PSV2;
+    PSV1.push_back(0);
+    PSV1.push_back(1);
+    PSV1.push_back(2);
+    assert(PSV1.size() == 3);
+    assert(PSV2.size() == 0);
+    std::swap(PSV1, PSV2);
+    assert(PSV1.size() == 0);
+    assert(PSV2.size() == 3);
+    int i = 0;
+    for (int x : PSV2) {
+      assert(x == i);
+      ++i;
+    }
+    for (int x : PSV1) {
+      assert(false);
+      (void)x;
+    }
+  }
+}
+
+int main(int, char**) {
+  testPODSmallVector();
+  return 0;
+}