Use type_traits to test if copyable/assignable

Replace compile tests that check if types are copy constructible and copy assignable with normal tests that use type_traits (if available).

test/format-test.cc

@@ -36,6 +36,10 @@
 #include <sstream>
 #include <stdint.h>
 
+#if FMT_USE_TYPE_TRAITS
+# include <type_traits>
+#endif
+
 #include "gmock/gmock.h"
 
 #include "format.h"
@@ -124,6 +128,16 @@ class TestString {
   }
 };
 
+#if FMT_USE_TYPE_TRAITS
+TEST(WriterTest, NotCopyConstructible) {
+  EXPECT_FALSE(std::is_copy_constructible<BasicWriter<char> >::value);
+}
+
+TEST(WriterTest, NotCopyAssignable) {
+  EXPECT_FALSE(std::is_copy_assignable<BasicWriter<char> >::value);
+}
+#endif
+
 TEST(WriterTest, Ctor) {
   MemoryWriter w;
   EXPECT_EQ(0u, w.size());