configure: Do not link all applications against libgsm

Use the same trick as done by the dlopen check to not
have everyone link against the library.

openbsc/configure.ac

@@ -63,7 +63,8 @@ AC_ARG_ENABLE([mgcp-transcoding], [AS_HELP_STRING([--enable-mgcp-transcoding], [
 AC_ARG_WITH([g729], [AS_HELP_STRING([--with-g729], [Enable G.729 encoding/decoding.])], [osmo_ac_with_g729="$withval"],[osmo_ac_with_g729="no"])
 
 if test "$osmo_ac_mgcp_transcoding" = "yes" ; then
-    AC_SEARCH_LIBS(gsm_create, gsm)
+    AC_SEARCH_LIBS([gsm_create], [gsm], [LIBRARY_GSM="$LIBS";LIBS=""])
+    AC_SUBST(LIBRARY_GSM)
     if test "$osmo_ac_with_g729" = "yes" ; then
 	PKG_CHECK_MODULES(LIBBCG729, libbcg729 >= 0.1, [AC_DEFINE([HAVE_BCG729], [1], [Use bgc729 decoder/encoder])])
     fi

openbsc/src/osmo-bsc_mgcp/Makefile.am

@@ -10,4 +10,5 @@ osmo_bsc_mgcp_SOURCES = mgcp_main.c
 osmo_bsc_mgcp_LDADD = $(top_builddir)/src/libcommon/libcommon.a \
 		 $(top_builddir)/src/libmgcp/libmgcp.a -lrt \
 		 $(LIBOSMOVTY_LIBS) $(LIBOSMOCORE_LIBS) \
-		 $(LIBOSMONETIF_LIBS) $(LIBBCG729_LIBS)
+		 $(LIBOSMONETIF_LIBS) $(LIBBCG729_LIBS) \
+		 $(LIBRARY_GSM)

openbsc/tests/mgcp/Makefile.am

@@ -25,4 +25,4 @@ mgcp_transcoding_test_LDADD = \
 		$(top_builddir)/src/libmgcp/libmgcp.a \
 		$(top_builddir)/src/libcommon/libcommon.a \
 		$(LIBOSMOCORE_LIBS) $(LIBBCG729_LIBS) -lrt -lm $(LIBOSMOSCCP_LIBS) $(LIBOSMOVTY_LIBS) \
-		$(LIBRARY_DL) $(LIBOSMONETIF_LIBS)
+		$(LIBRARY_DL) $(LIBOSMONETIF_LIBS) $(LIBRARY_GSM)