Update Makefile.am

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
diff --git a/.gitignore b/.gitignore
index c89e9b0..db2ef01 100644
--- a/.gitignore
+++ b/.gitignore
@@ -59,3 +59,4 @@
 tests/testsuite.log
 
 writtenconfig/
+libintern.la