Fixed Clang 5.0 compile errors (#4085)

* Fixed Clang 5.0 compile errors

* Fixed wrong comment

* Only disable warnings in Clang 5 or higher

* Added a CMake condition for the Clang 5 no-zero-as-null-pointer-constant warning

* Now using the use_nullptr branch of the Cuberite specific SQLiteCpp fork

src/main.cpp

@@ -72,6 +72,12 @@ bool cRoot::m_RunAsService = false;
 
 
 #ifndef _DEBUG
+// Because SIG_DFL or SIG_IGN could be NULL instead of nullptr, we need to disable the Clang warning here
+#if __clang_major__ >= 5
+	#pragma clang diagnostic push
+	#pragma clang diagnostic ignored "-Wzero-as-null-pointer-constant"
+#endif
+
 static void NonCtrlHandler(int a_Signal)
 {
 	LOGD("Terminate event raised from std::signal");
@@ -115,6 +121,10 @@ static void NonCtrlHandler(int a_Signal)
 		default: break;
 	}
 }
+
+#if __clang_major__ >= 5
+	#pragma clang diagnostic pop
+#endif
 #endif  // _DEBUG