[PATCH] Improve tests for std::add_pointer

[Jonathan Wakely]

The type trait depends on is_void so the tests should check those cases.

	* testsuite/20_util/add_pointer/value.cc: Check void types.

Tested x86_64-linux, committed to trunk.

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commit 5b35f49aeb052513b4580ed4d9ea0ef3118a200d
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Oct 31 14:05:47 2019 +0000

    Improve tests for std::add_pointer
    
    The type trait depends on is_void so the tests should check those cases.
    
            * testsuite/20_util/add_pointer/value.cc: Check void types.

diff --git a/libstdc++-v3/testsuite/20_util/add_pointer/value.cc b/libstdc++-v3/testsuite/20_util/add_pointer/value.cc
index acf9442851f..66d94783c11 100644
--- a/libstdc++-v3/testsuite/20_util/add_pointer/value.cc
+++ b/libstdc++-v3/testsuite/20_util/add_pointer/value.cc
@@ -31,8 +31,14 @@ void test01()
   static_assert(is_same<add_pointer<const int>::type, const int*>::value, "");
   static_assert(is_same<add_pointer<int&>::type, int*>::value, "");
   static_assert(is_same<add_pointer<ClassType*>::type,
-		ClassType**>::value, "");
+			ClassType**>::value, "");
   static_assert(is_same<add_pointer<ClassType>::type, ClassType*>::value, "");
+  static_assert(is_same<add_pointer<void>::type, void*>::value, "");
+  static_assert(is_same<add_pointer<const void>::type, const void*>::value, "");
+  static_assert(is_same<add_pointer<volatile void>::type,
+			volatile void*>::value, "");
+  static_assert(is_same<add_pointer<const volatile void>::type,
+			const volatile void*>::value, "");
 }
 
 void test02()