prefix sub-directories containing libraries with 'lib'

... and make sure tests work again after restructuring
diff --git a/openbsc/src/osmo-bsc/Makefile.am b/openbsc/src/osmo-bsc/Makefile.am
index 735d440..95b9ef4 100644
--- a/openbsc/src/osmo-bsc/Makefile.am
+++ b/openbsc/src/osmo-bsc/Makefile.am
@@ -9,6 +9,10 @@
 		   osmo_bsc_grace.c osmo_bsc_msc.c osmo_bsc_sccp.c \
 		   osmo_bsc_filter.c osmo_bsc_bssap.c osmo_bsc_audio.c
 # once again since TRAU uses CC symbol :(
-osmo_bsc_LDADD = ../bsc/libbsc.a ../msc/libmsc.a ../bsc/libbsc.a \
-		../abis/libabis.a ../trau/libtrau.a ../common/libcommon.a \
+osmo_bsc_LDADD = $(top_builddir)/src/libbsc/libbsc.a \
+		 $(top_builddir)/src/libmsc/libmsc.a \
+		 $(top_builddir)/src/libbsc/libbsc.a \
+		 $(top_builddir)/src/libabis/libabis.a \
+		 $(top_builddir)/src/libtrau/libtrau.a \
+		 $(top_builddir)/src/libcommon/libcommon.a \
 		 $(LIBOSMOSCCP_LIBS)