Add Linux Mint support

[fgaz]

Mint is basically like ubuntu, so I just set the same urls.

Thanks to @L0cutus for helping me test this

[fgaz]

This is the error current ghcup gives on linux mint:

/home/l0cutus/.ghcup/ghc/8.6.3/lib/ghc-8.6.3/bin/ghc-pkg: error while loading shared libraries: libtinfo.so.6: cannot open shared object file: No such file or directory
ghc.mk:985: recipe for target 'install_packages' failed
make[1]: *** [install_packages] Error 127
Makefile:51: recipe for target 'install' failed
make: *** [install] Error 2
Failed to install, consider updating this script via: ghcup upgrade
"ghcup --cache install" failed!

This got me thinking: could we detect whether to fall back to the deb or the fedora version by looking at the presence or absence of libtinfo.so.6?

[hvr]

This got me thinking: could we detect whether to fall back to the deb or the fedora version by looking at the presence or absence of libtinfo.so.6?

ghcup follows the paradigm to make that decision which bindist to pick based on the distribution name/release reported by lsb_release/uname/os-release; testing the environment for the presence of particular properties such as libraries etc represents a different paradigm which isn't in scope for ghcup.

[fgaz]

@hvr

Makes sense. I can see it could quickly become a slippery slope.

Then I guess it could be a good idea to add a notice if the os is unknown and the installation fails. Something like

Notice: You are using an unsupported/unrecognized operating system, which could have caused the failure. Please consider reporting it to [issues url] or adding support for your OS to ghcup by sending a pr to [pr url]