Enable deprecation warnings

[DaAwesomeP]

It seems that we missed a lot of the deprecation warnings because they were turned off. Now that we have settled on minimum compiler support in #2005, it seems appropriate to turn these on and not ignore them. If we run into something specific that is deprecated in modern GCC/Clang but has no replacement for the minimum compiler version we support, we can handle those case-by-case.

The build for this PR will intentionally fail until many of @aroffringa's PRs are merged. Once those are merged I will rebase and we can see if we missed anything.

[aroffringa]

Good idea. I see in your changes the warnings were disabled in CI, but not on a normal build (those related to a normal build were all -Wno-error options). If I do a local build with mine and your changes combined I don't see warnings.

I can't approve, but the changes look fine to me once the warning fixes are merged.

[DaAwesomeP]

I see in your changes the warnings were disabled in CI, but not on a normal build (those related to a normal build were all -Wno-error options).

The GNU_PLUS_PLUS_11_DEPRECATIONS part was enabling -Wno-error=deprecated-declarations for local builds as well. If I try build now locally it doesn't get very far and runs into std::binary_function and std::auto_ptr.

If I do a local build with mine and your changes combined I don't see warnings.

Yay! That means you found everything.

[aroffringa]

@nomis52 be aware that by merging this, a standard

./configure
make

in the source dir fails to compile now, so the fixes #1890 and #1889 have to be merged to repair such a master build...