switch sqlite3 to single-threaded mode

Looking at 'perf top' of osmo-msc under load shows that there's a
significant amount of time spent in terms of locking (mutex,...)
which is useless as osmo-msc is a single-threaded application.

Unfortunately libdbi doesn't provide a mechanism to perform
sqlite3_config(), so we have to do it directly here, introducing an
explicit build-time dependency (and linkage) to libsqlite3.

Related: OS#5559
Change-Id: I5bbea90d28b6d73b64b9e5124ff59304b90a8a75
diff --git a/tests/db_sms/Makefile.am b/tests/db_sms/Makefile.am
index 52fd35e..52e8cab 100644
--- a/tests/db_sms/Makefile.am
+++ b/tests/db_sms/Makefile.am
@@ -17,6 +17,7 @@
 	$(LIBSMPP34_CFLAGS) \
 	$(LIBOSMOMGCPCLIENT_CFLAGS) \
 	$(LIBOSMOGSUPCLIENT_CFLAGS) \
+	$(LIBSQLITE3_CFLAGS) \
 	$(NULL)
 
 EXTRA_DIST = \
@@ -46,6 +47,7 @@
 	$(LIBASN1C_LIBS) \
 	$(LIBOSMOMGCPCLIENT_LIBS) \
 	$(LIBOSMOGSUPCLIENT_LIBS) \
+	$(LIBSQLITE3_LIBS) \
 	$(LIBRARY_GSM) \
 	-ldbi \
 	$(NULL)