guile: handle readline support explicitly

Otherwise the host readline (+ncurses) development files can poison the
build causing breakage. Fixes:
http://autobuild.buildroot.net/results/d0a/d0a8ad9d3f19592e06df36408d6af745f7908165/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/guile/guile.mk

@@ -32,6 +32,16 @@ ifeq ($(BR2_STATIC_LIBS),y)
 GUILE_CFLAGS += -DGC_NO_DLOPEN
 endif
 
+# It can use readline, but on the condition that it was build against
+# ncurses. If both aren't present disable readline support since the
+# host readline/ncurses support can poison the build.
+ifeq ($(BR2_PACKAGE_NCURSES)$(BR2_PACKAGE_READLINE),yy)
+GUILE_CONF_OPTS += --with-libreadline-prefix=$(STAGING_DIR)/usr
+GUILE_DEPENDENCIES += readline
+else
+GUILE_CONF_OPTS += --without-libreadline-prefix
+endif
+
 GUILE_CONF_ENV += GUILE_FOR_BUILD=$(HOST_DIR)/usr/bin/guile \
 	CFLAGS="$(TARGET_CFLAGS) $(GUILE_CFLAGS)"