Fix AppImages for distros that are not ubuntu 14.04

[hcorion]

Fixes #4414 and possible also 4427, though I think that's a different issue.

Basically, this makes libstdc++6 load only ubuntu 14.04, and uses the distros's lib otherwise.
If you want more details on the actual implementation, check out:
darealshinji/linuxdeploy-plugin-checkrt@master...RPCS3:master

[mads256h]

This should maybe point to a more trusted repo preferably from rpcs3 themselves.

[hcorion]

I don't have the rights to add a repo, but if Neko feels it is neccesary, I wouldn't be against it.

[sibradzic]

it didnt fix Ubuntu 18.04, black screen on any game run... The latest build that works reliably is 6638.
I could make it work by extracting AppImages ard running it locally with LD_LIBRARY_PATH=squashfs-root/usr/lib, and wiping out all libs other than libQt5*, libicu* & libpng*. I'll try to rule out which particular lib breaks the RPCS3...

[Caliel666]

didn't fix for ubuntu 17.10

[sibradzic]

On Ubuntu 18.04 its AppImages static libglapi.so.0 that causes black screen in all games, removing it from LD_LIBRARY_PATH makes everything get back to normal.
BTW, following the AppImages extraction, it totally seems that there are way too many static libs packed in, IMHO, other than the latest Qt none of that makes too much sense (why there are two different versions of libpng packed in?!). Maybe AppIamge binary should only contain the very essential libs, and the rest would be provided by the distro itself?

Isn't it time to start building proper distro package releases for RPCS3?

[hcorion]

@sibradzic can you make the same comment on the relevant issue, #4427, so we don't have this conversation scattered all over the place. I'll reply to you there.