Initial patch from Anna "CyberTailor", tweaked by me (drop guessing_* and always append CFLAGS)

but still try to autodetect with pkg-config if they aren't provided. Passing CFLAGS/LDFLAGS from the command line will still override the guessed ones.

we need to delete the events associated with the backends, otherwise the server process won't ever quit. Here, we add a pending counter to every backend and shut down immediately if they aren't handling any client; otherwise we try to close them as soon as possible (i.e. when they close the connection to the last connected client.)

our stderr could have been sent to the logger process, so it may be invalid. Furthermore, in the future we may want to capture also the stderr of the processes.

otherwise path, port and/or prog could become an invalid pointer.

before we matched ppc64le as ppc64 (which is big ending I presume), so the seccomp filter would always kill gmid #4 related

`printf | openssl` is ugly :/