The simple_ctrl.c is used by 2 independent binaries. Let's build it as a
convenience libtool library [1] to make it easier to add further
external dependencies in future.
While at it, also move osmo-sysmon dependencies to program-specific
_CFLAGS from generic one.
[1] https://www.gnu.org/software/automake/manual/html_node/Libtool-Convenience-Libraries.html
Change-Id: Idfaba17b54983709278e1c24bf55edbbb4abd961
Moving configuration data from anonymous struct into shared header as a
preparation for ctrl logging improvements in follow-up patches.
Change-Id: I3520e14ca6e1b8e270dbd4b1bf2378fe486991ce
Related: SYS#2655