prefix sub-directories containing libraries with 'lib'

... and make sure tests work again after restructuring
diff --git a/openbsc/src/utils/Makefile.am b/openbsc/src/utils/Makefile.am
index 2847c6a..2351f8a 100644
--- a/openbsc/src/utils/Makefile.am
+++ b/openbsc/src/utils/Makefile.am
@@ -5,6 +5,8 @@
 bin_PROGRAMS = bs11_config isdnsync
 
 bs11_config_SOURCES = bs11_config.c rs232.c
-bs11_config_LDADD = ../common/libcommon.a ../abis/libabis.a ../bsc/libbsc.a
+bs11_config_LDADD = $(top_builddir)/src/libcommon/libcommon.a \
+		    $(top_builddir)/src/libabis/libabis.a \
+		    $(top_builddir)/src/libbsc/libbsc.a
 
 isdnsync_SOURCES = isdnsync.c