Fix some warnings and wrap ESP8266 Client overrides in #ifdef

[sandeepmistry]

Based on the discussions in:

• Providing empty functions for functions defined pure virtual in ESP8266::Client.h #18 (comment)
• ade2940#commitcomment-35852164

@lxrobotics for @JAndrassy's concerns, to reproduce, use the WiFiEcho.ino and change:

const char broker[] = "test.mosquitto.org";

to

IPAddress broker = IPAddress(10, 0, 1, 1);

You will get a compile error.

[JAndrassy]

the invalid pure virtual functions were only in esp8266 core 2.5.0. they were reverted in 2.5.1 in May, current version of esp8266 core is 2.6.1

[sandeepmistry]

@JAndrassy is there some way to determine the core version at compile time?

[JAndrassy]

@JAndrassy is there some way to determine the core version at compile time?

why is the compatibility with broken 2.5.0 important?

[sandeepmistry]

why is the compatibility with broken 2.5.0 important?

@JAndrassy I'm not sure, there is only a comment from @lxrobotics: ade2940#commitcomment-35808711 that Create needs it.

@lxrobotics and/or @eclipse1985 could you please explain?

[eclipse1985]

We have to keep the compatibility with 2.5.0 because on create we are locked at this version. Versions >2.5 have totally changed the build/upload tools, and we are unable to port them on create agent right now.

[JAndrassy]

We have to keep the compatibility with 2.5.0 because on create we are locked at this version. Versions >2.5 have totally changed the build/upload tools, and we are unable to port them on create agent right now.

esp8266 core 2.4.2 is a very good version. 2.5.0 updated to Espressif SDK 3.0 beta and it doesn't work good. they reverted to SDK 2.2.x in 2.5.1

[aentinger]

@JAndrassy Thank you for letting us know. I suppose the virtual function declarations causing this change are still defined in ESP8266 Core 2.4.2 Client class?

[JAndrassy]

@JAndrassy Thank you for letting us know. I suppose the virtual function declarations causing this change are still defined in ESP8266 Core 2.4.2 Client class?

they are not. Only 2.5.0 is wrong.

[aentinger]

@eclipse1985 How about downgrading to 2.4.2 then?

[eclipse1985]

I'm not sure this is feasible on create side cc @rsora @matteosuppo

[aentinger]

Approving this since we are stuck with the 2.5.0 version on create for now.