Add configure option to skip subdirectories

If you pass --enable-skip-subdirectories then configure will skip
configuring or reconfiguring libraries and simply configure the FS
core itself.

configure.in

@@ -330,6 +330,11 @@ if test "x${enable_visibility}" != "xno" ; then
 	fi
 fi
 
+# Option to skip configuration of subdirectories
+AC_ARG_ENABLE(skip-subdirectories,
+[AC_HELP_STRING([--enable-skip-subdirectories],[skip configuration of subdirectories])],
+[enable_skip_subdirectories="$enableval"],[enable_skip_subdirectories="no"])
+
 # Enable ClueCon nag banner (default: on)
 AC_ARG_ENABLE(huge-cluecon-nag,
 [AC_HELP_STRING([--disable-huge-cluecon-nag],[build without huge ClueCon banners])],
@@ -1089,38 +1094,39 @@ ac_configure_args="$ac_configure_args CONFIGURE_CFLAGS='$CFLAGS' CONFIGURE_CXXFL
 #	--localstatedir='$localstatedir' --datadir='$datadir'"
 
 # Run configure in all the subdirs
-AC_CONFIG_SUBDIRS([libs/srtp])
-AC_CONFIG_SUBDIRS([libs/sqlite])
-if test "$enable_core_libedit_support" = "yes" ; then
-    AC_CONFIG_SUBDIRS([libs/libedit])
-fi
-
-AC_CONFIG_SUBDIRS([libs/pcre])
-AC_CONFIG_SUBDIRS([libs/apr])
-AC_CONFIG_SUBDIRS([libs/apr-util])
-AC_CONFIG_SUBDIRS([libs/ilbc])
-AC_CONFIG_SUBDIRS([libs/curl])
-AC_CONFIG_SUBDIRS([libs/iksemel])
-AC_CONFIG_SUBDIRS([libs/js/nsprpub])
-AC_CONFIG_SUBDIRS([libs/js])
-AC_CONFIG_SUBDIRS([libs/libdingaling])
-AC_CONFIG_SUBDIRS([libs/libsndfile])
-AC_CONFIG_SUBDIRS([libs/sofia-sip])
-AC_CONFIG_SUBDIRS([libs/speex])
-AC_CONFIG_SUBDIRS([libs/portaudio])
-AC_CONFIG_SUBDIRS([libs/openzap])
-AC_CONFIG_SUBDIRS([libs/freetdm])
-AC_CONFIG_SUBDIRS([libs/unimrcp])
-AC_CONFIG_SUBDIRS([libs/tiff-4.0.2])
-AC_CONFIG_SUBDIRS([libs/spandsp])
-AC_CONFIG_SUBDIRS([libs/broadvoice])
-AC_CONFIG_SUBDIRS([libs/libg722_1])
-AC_CONFIG_SUBDIRS([libs/silk])
-AC_CONFIG_SUBDIRS([libs/libcodec2])
-if test "x${enable_zrtp}" = "xyes"; then
-   AC_CONFIG_SUBDIRS([libs/libzrtp/projects/gnu])
+if ! test "${enable_skip_subdirectories}" = "yes"; then
+   AC_CONFIG_SUBDIRS([libs/srtp])
+   AC_CONFIG_SUBDIRS([libs/sqlite])
+   if test "$enable_core_libedit_support" = "yes" ; then
+      AC_CONFIG_SUBDIRS([libs/libedit])
+   fi
+   AC_CONFIG_SUBDIRS([libs/pcre])
+   AC_CONFIG_SUBDIRS([libs/apr])
+   AC_CONFIG_SUBDIRS([libs/apr-util])
+   AC_CONFIG_SUBDIRS([libs/ilbc])
+   AC_CONFIG_SUBDIRS([libs/curl])
+   AC_CONFIG_SUBDIRS([libs/iksemel])
+   AC_CONFIG_SUBDIRS([libs/js/nsprpub])
+   AC_CONFIG_SUBDIRS([libs/js])
+   AC_CONFIG_SUBDIRS([libs/libdingaling])
+   AC_CONFIG_SUBDIRS([libs/libsndfile])
+   AC_CONFIG_SUBDIRS([libs/sofia-sip])
+   AC_CONFIG_SUBDIRS([libs/speex])
+   AC_CONFIG_SUBDIRS([libs/portaudio])
+   AC_CONFIG_SUBDIRS([libs/openzap])
+   AC_CONFIG_SUBDIRS([libs/freetdm])
+   AC_CONFIG_SUBDIRS([libs/unimrcp])
+   AC_CONFIG_SUBDIRS([libs/tiff-4.0.2])
+   AC_CONFIG_SUBDIRS([libs/spandsp])
+   AC_CONFIG_SUBDIRS([libs/broadvoice])
+   AC_CONFIG_SUBDIRS([libs/libg722_1])
+   AC_CONFIG_SUBDIRS([libs/silk])
+   AC_CONFIG_SUBDIRS([libs/libcodec2])
+   if test "x${enable_zrtp}" = "xyes"; then
+      AC_CONFIG_SUBDIRS([libs/libzrtp/projects/gnu])
+   fi
+   AC_CONFIG_SUBDIRS([libs/libwebsockets])
 fi
-AC_CONFIG_SUBDIRS([libs/libwebsockets])
 
 case $host in
    *-openbsd*)