finish openbsc / libosmocore separation

* use pkg-config from openbsc to find header and library
* move sms and timer tests to libosmocore itself
* ensure "make distcheck" works on both packages
diff --git a/libosmocore/libosmocore.pc.in b/libosmocore/libosmocore.pc.in
index 0d09cb8..7c29869 100644
--- a/libosmocore/libosmocore.pc.in
+++ b/libosmocore/libosmocore.pc.in
@@ -1,4 +1,5 @@
-prefix=@exec_prefix@
+prefix=@prefix@
+exec_prefix=@exec_prefix@
 libdir=@libdir@
 includedir=@includedir@