make libosmo-mgcp.a an .la lib

.la libs aka LTLIB can include library dependencies.

Rationale: An upcoming patch adds noinst libosmo-sdp, used by both
osmo-mgw and libosmo-mgcp-client, and the cleanest way to link that is
via a library dependency. Prepare for that.

Change-Id: I5302d56e571d0da9061c275ce13d4f085c044671

src/libosmo-mgcp/Makefile.am

@@ -19,15 +19,15 @@ AM_LDFLAGS = \
 	$(COVERAGE_LDFLAGS) \
 	$(NULL)
 
-noinst_LIBRARIES = \
-	libosmo-mgcp.a \
+noinst_LTLIBRARIES = \
+	libosmo-mgcp.la \
 	$(NULL)
 
 noinst_HEADERS = \
 	g711common.h \
 	$(NULL)
 
-libosmo_mgcp_a_SOURCES = \
+libosmo_mgcp_la_SOURCES = \
 	mgcp_protocol.c \
 	mgcp_network.c \
 	mgcp_vty.c \
@@ -43,3 +43,12 @@ libosmo_mgcp_a_SOURCES = \
 	mgcp_e1.c \
 	mgcp_iuup.c \
 	$(NULL)
+
+libosmo_mgcp_la_LIBADD = \
+	$(LIBOSMOCORE_LIBS) \
+	$(LIBOSMOGSM_LIBS) \
+	$(LIBOSMOVTY_LIBS) \
+	$(LIBOSMONETIF_LIBS) \
+	$(LIBOSMOABIS_LIBS) \
+	$(LIBOSMOTRAU_LIBS) \
+	$(NULL)

src/osmo-mgw/Makefile.am

@@ -25,12 +25,6 @@ osmo_mgw_SOURCES = \
 	$(NULL)
 
 osmo_mgw_LDADD = \
-	$(top_builddir)/src/libosmo-mgcp/libosmo-mgcp.a \
-	$(LIBOSMOCORE_LIBS) \
-	$(LIBOSMOVTY_LIBS) \
-	$(LIBOSMOGSM_LIBS) \
+	$(top_builddir)/src/libosmo-mgcp/libosmo-mgcp.la \
 	$(LIBOSMOCTRL_LIBS) \
-	$(LIBOSMONETIF_LIBS) \
-	$(LIBOSMOABIS_LIBS) \
-	$(LIBOSMOTRAU_LIBS) \
 	$(NULL)

tests/mgcp/Makefile.am

@@ -34,7 +34,7 @@ mgcp_test_SOURCES = \
 	$(NULL)
 
 mgcp_test_LDADD = \
-	$(top_builddir)/src/libosmo-mgcp/libosmo-mgcp.a \
+	$(top_builddir)/src/libosmo-mgcp/libosmo-mgcp.la \
 	$(LIBOSMOCORE_LIBS) \
 	$(LIBOSMOVTY_LIBS) \
 	$(LIBOSMOGSM_LIBS) \