sccp: Use the external libosmo-sccp as sccp implementation

Add --enable-nat and --enable-osmo-bsc to build applications
requiring the Osmo SCCP library to be installed. We are not
using autodiscover as this is out of fashion.
diff --git a/openbsc/configure.in b/openbsc/configure.in
index 50189a4..b877e6b 100644
--- a/openbsc/configure.in
+++ b/openbsc/configure.in
@@ -22,6 +22,27 @@
 
 AM_CONDITIONAL(HAVE_LIBGTP, test "x$GPRS_LIBGTP" != "x")
 
+
+AC_ARG_ENABLE([nat], [AS_HELP_STRING([--enable-nat], [Build the BSC NAT. Requires SCCP])],
+    [
+        PKG_CHECK_MODULES(LIBOSMOSCCP, libosmo-sccp)
+        osmo_ac_build_nat="yes"
+    ],
+    [
+        osmo_ac_build_nat="no"
+    ])
+AM_CONDITIONAL(BUILD_NAT, test "x$osmo_ac_build_nat" = "xyes")
+
+AC_ARG_ENABLE([osmo-bsc], [AS_HELP_STRING([--enable-bsc], [Build the Osmo BSC])],
+    [
+        PKG_CHECK_MODULES(LIBOSMOSCCP, libosmo-sccp)
+        osmo_ac_build_bsc="yes"
+    ],
+    [
+        osmo_ac_build_bsc="no"
+    ])
+AM_CONDITIONAL(BUILD_BSC, test "x$osmo_ac_build_bsc" = "xyes")
+
 PKG_CHECK_MODULES(LIBOSMOCORE, libosmocore >= 0.1.15)
 PKG_CHECK_MODULES(LIBOSMOVTY, libosmovty >= 0.1.9)
 
@@ -47,9 +68,7 @@
 
 AC_OUTPUT(
     openbsc.pc
-    libsccp.pc
     include/openbsc/Makefile
-    include/sccp/Makefile
     include/Makefile
     src/Makefile
     src/ipaccess/Makefile
@@ -61,6 +80,5 @@
     tests/gsm0408/Makefile
     tests/db/Makefile
     tests/channel/Makefile
-    tests/sccp/Makefile
     tests/bsc-nat/Makefile
     Makefile)