[libc++abi] Avoid including source files into unittest_demangle

[ldionne]

Summary

That is not necessary to test what we're testing, and in fact including
abort_message.cpp into that file caused some link errors if we didn't
link some of the dependencies of libc++abi directly into the test.

[nickdesaulniers]

Sorry about that! Thanks for the patch!

libcxxabi/test/unittest_demangle.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // 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 "../src/cxa_demangle.cpp"
-#include "../src/abort_message.cpp"
+#include <cassert>
+#include <utility>
 
-using namespace __cxxabiv1;
+#include "../src/demangle/ItaniumDemangle.h"
 
 void testPODSmallVector() {
   { // {push/pop}_back
-    PODSmallVector<int, 1> PSV;
+    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);
   }
 
   {
-    PODSmallVector<int, 1> PSV1;
+    itanium_demangle::PODSmallVector<int, 1> PSV1;
     PSV1.push_back(1);
     PSV1.push_back(2);
     PSV1.push_back(3);
 
-    PODSmallVector<int, 1> PSV2;
+    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);
   }
 
   {
-    PODSmallVector<int, 10> PSV1;
-    PODSmallVector<int, 10> PSV2;
+    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);