Remove copy constructor to make flatbuffers struct trivially copyable… (#4476)

* Remove copy constructor to make flatbuffers struct trivially copyable + add tests.

* Add support non c++11 compliant compilers.

* Fix std::trivially_copyiable test for non-C++11 compliant compilers.

* Fix trivially_copyable not part of glibc < 5 even with c++11 switch enabled.

tests/test.cpp

@@ -526,6 +526,18 @@ void SizePrefixedTest() {
   TEST_EQ_STR(m->name()->c_str(), "bob");
 }
 
+
+void TriviallyCopyableTest() {
+  #if __GNUG__ && __GNUC__ < 5
+    TEST_EQ(__has_trivial_copy(Vec3), true);
+  #else
+    #if __cplusplus >= 201103L
+      TEST_EQ(std::is_trivially_copyable<Vec3>::value, true);
+    #endif
+  #endif
+}
+
+
 // example of parsing text straight into a buffer, and generating
 // text back from it:
 void ParseAndGenerateTextTest() {
@@ -1809,6 +1821,9 @@ int main(int /*argc*/, const char * /*argv*/[]) {
   #else
     auto &flatbuf = flatbuf1;
   #endif // !defined(FLATBUFFERS_CPP98_STL)
+
+  TriviallyCopyableTest();
+
   AccessFlatBufferTest(reinterpret_cast<const uint8_t *>(rawbuf.c_str()),
                        rawbuf.length());
   AccessFlatBufferTest(flatbuf.data(), flatbuf.size());