prefix sub-directories containing libraries with 'lib'

... and make sure tests work again after restructuring
diff --git a/openbsc/src/gprs/Makefile.am b/openbsc/src/gprs/Makefile.am
index e981115..16c2200 100644
--- a/openbsc/src/gprs/Makefile.am
+++ b/openbsc/src/gprs/Makefile.am
@@ -11,9 +11,12 @@
 endif
 
 osmo_gbproxy_SOURCES = gb_proxy.c gb_proxy_main.c gb_proxy_vty.c
-osmo_gbproxy_LDADD = $(top_builddir)/src/gb/libgb.a $(top_builddir)/src/common/libcommon.a
+osmo_gbproxy_LDADD = 	$(top_builddir)/src/libgb/libgb.a \
+			$(top_builddir)/src/libcommon/libcommon.a
 
 osmo_sgsn_SOURCES =	gprs_gmm.c gprs_sgsn.c gprs_sndcp.c gprs_sndcp_vty.c \
 			sgsn_main.c sgsn_vty.c sgsn_libgtp.c \
 			gprs_llc.c gprs_llc_vty.c crc24.c
-osmo_sgsn_LDADD = $(top_builddir)/src/gb/libgb.a $(top_builddir)/src/common/libcommon.a -lgtp
+osmo_sgsn_LDADD = 	$(top_builddir)/src/libgb/libgb.a \
+			$(top_builddir)/src/libcommon/libcommon.a \
+			-lgtp