split 'libosmocore' from openbsc codebase

This library is intended to collect all generic/common funcitionality
of all Osmocom.org projects, including OpenBSC but also OsmocomBB

The library currently includes the following modules:

bitvec, comp128, gsm_utils, msgb, select, signal, statistics, talloc, timer,
tlv_parse, linuxlist

msgb allocation error debugging had to be temporarily disabled as it depends on
'debug.c' functionality which at the moment remains in OpenBSC
diff --git a/openbsc/src/silent_call.c b/openbsc/src/silent_call.c
index a0c166e..cada24e 100644
--- a/openbsc/src/silent_call.c
+++ b/openbsc/src/silent_call.c
@@ -25,7 +25,7 @@
 #include <unistd.h>
 #include <errno.h>
 
-#include <openbsc/msgb.h>
+#include <osmocore/msgb.h>
 #include <openbsc/signal.h>
 #include <openbsc/debug.h>
 #include <openbsc/paging.h>