[build] Create a libbsc.a as noinst_LIBRARY, link bsc_hack and tests against it

Link the tests against the libbsc.a to avoid most of the breakage
when creating new symbols.
diff --git a/src/Makefile.am b/src/Makefile.am
index f89836c..412e1e3 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -2,13 +2,16 @@
 AM_CFLAGS=-Wall
 
 sbin_PROGRAMS = bsc_hack bs11_config ipaccess-find
+noinst_LIBRARIES = libbsc.a
 
-bsc_hack_SOURCES = bsc_hack.c abis_rsl.c abis_nm.c gsm_04_08.c gsm_data.c \
+libbsc_a_SOURCES = abis_rsl.c abis_nm.c gsm_04_08.c gsm_data.c \
 		gsm_subscriber.c msgb.c select.c chan_alloc.c timer.c debug.c db.c \
 		gsm_04_11.c telnet_interface.c telnet_parser.l subchan_demux.c \
 		trau_frame.c trau_mux.c paging.c e1_config.c e1_input.c tlv_parser.c \
 		input/misdn.c input/ipaccess.c signal.c gsm_utils.c
-bsc_hack_LDADD = -ldl -ldbi
+
+bsc_hack_SOURCES = bsc_hack.c
+bsc_hack_LDADD = libbsc.a -ldl -ldbi
 
 bs11_config_SOURCES = bs11_config.c abis_nm.c gsm_data.c msgb.c debug.c select.c timer.c rs232.c tlv_parser.c