configure.ac: Add --disable-remsim-server

This allows builds on small/embedded platforms to avoid all the
dependencies required by remsim-server, including ulfius, yder, etc.

Closes: OS#3896
Change-Id: I2b1ec8a9a88b931ac56a63df88886e37c580a92b
diff --git a/src/Makefile.am b/src/Makefile.am
index d671f37..5b6efb9 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -1,4 +1,7 @@
-SUBDIRS = rspro server
+SUBDIRS = rspro
+if BUILD_SERVER
+SUBDIRS += server
+endif
 
 AM_CFLAGS = -Wall -I$(top_srcdir)/include -I$(top_builddir)/include \
 	    $(OSMOCORE_CFLAGS) $(OSMOGSM_CFLAGS) $(OSMOABIS_CFLAGS) \