prefix sub-directories containing libraries with 'lib'

... and make sure tests work again after restructuring
diff --git a/openbsc/tests/debug/Makefile.am b/openbsc/tests/debug/Makefile.am
index 8423fd1..47437b1 100644
--- a/openbsc/tests/debug/Makefile.am
+++ b/openbsc/tests/debug/Makefile.am
@@ -2,5 +2,6 @@
 AM_CFLAGS=-Wall $(LIBOSMOCORE_CFLAGS)
 noinst_PROGRAMS = debug_test
 
-debug_test_SOURCES = debug_test.c $(top_srcdir)/src/debug.c 
-debug_test_LDADD = $(LIBOSMOCORE_LIBS)
+debug_test_SOURCES = debug_test.c
+debug_test_LDADD = 	$(LIBOSMOCORE_LIBS) \
+			$(top_srcdir)/src/libcommon/libcommon.a