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.