Add defaulted copy and move operations to format_error and system_error (#1347)

* Avoid weak vtables by providing a private virtual member function

* Add warning Wweak-vtables to clang when FMT_PEDANTIC is on

* Add defaulted copy and move operations to format_error and system_error

Compiler generated copy operations are deprecated and move operations
are not generated altogether.

* Add warning Wdeprecated to clang when FMT_PEDANTIC is on

2 files changed, 10 insertions, 0 deletions

diff --git a/test/core-test.cc b/test/core-test.cc
index 76612b99..931f44b7 100644
--- a/test/core-test.cc
+++ b/test/core-test.cc
@@ -127,8 +127,13 @@ TEST(BufferTest, Ctor) {
 struct dying_buffer : test_buffer<int> {
   MOCK_METHOD0(die, void());
   ~dying_buffer() { die(); }
+
+ private:
+  virtual void avoid_weak_vtable();
 };
 
+void dying_buffer::avoid_weak_vtable() {}
+
 TEST(BufferTest, VirtualDtor) {
   typedef StrictMock<dying_buffer> stict_mock_buffer;
   stict_mock_buffer* mock_buffer = new stict_mock_buffer();
diff --git a/test/test-assert.h b/test/test-assert.h
index 034a4ce6..c02dc0f2 100644
--- a/test/test-assert.h
+++ b/test/test-assert.h
@@ -14,8 +14,13 @@
 class assertion_failure : public std::logic_error {
  public:
   explicit assertion_failure(const char* message) : std::logic_error(message) {}
+
+ private:
+  virtual void avoid_weak_vtable();
 };
 
+void assertion_failure::avoid_weak_vtable() {}
+
 #define FMT_ASSERT(condition, message) \
   if (!(condition)) throw assertion_failure(message);