[APInt] Allow self-assignment with libstdc++

http://lab.llvm.org:8011/builders/llvm-clang-x86_64-expensive-checks-ubuntu/builds/8256/steps/test-check-all/logs/FAIL%3A%20LLVM%3A%3Athinlto-function-summary-paramaccess.ll

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D86053
diff --git a/llvm/unittests/ADT/APIntTest.cpp b/llvm/unittests/ADT/APIntTest.cpp
index 37ab21b..4b8e8c7 100644
--- a/llvm/unittests/ADT/APIntTest.cpp
+++ b/llvm/unittests/ADT/APIntTest.cpp
@@ -1783,8 +1783,9 @@
   }
 }
 
-// Test that self-move works, but only when we're using MSVC.
-#if defined(_MSC_VER)
+// Test that self-move works with EXPENSIVE_CHECKS. It calls std::shuffle which
+// does self-move on some platforms.
+#ifdef EXPENSIVE_CHECKS
 #if defined(__clang__)
 // Disable the pragma warning from versions of Clang without -Wself-move
 #pragma clang diagnostic push
@@ -1813,7 +1814,7 @@
 #pragma clang diagnostic pop
 #pragma clang diagnostic pop
 #endif
-#endif // _MSC_VER
+#endif // EXPENSIVE_CHECKS
 
 TEST(APIntTest, byteSwap) {
   EXPECT_EQ(0x00000000, APInt(16, 0x0000).byteSwap());