Add additional CI targets

[guijan]

Add additional CI targets:

• PCC: Need to wait until a version with this bug fixed is available.
• Termux: Has problems installing packages due to user permissions. (See also: Add Termux to CI #316)
• Cproc: C11 compiler, but scrot doesn't use VLAs, so our code should work in C11 mode too.
• Illumos or some Solaris based system.

[N-R-K]

Changed this into a meta-issue, individual issues for small things like this got a bit annoying.

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And btw, we can also just build PCC from a known working commit and use that. No need to wait for it to be packaged. We kinda did this for tcc in the nsxiv CI because ubuntu tcc was too old and buggy.

(This is of course assuming building PCC is fast and simple, similar to TCC).

[N-R-K]

Possible to add Illumos or some Solaris based system to the CI as well?