build: Set libsoup min/max defines

So we don't get warnings about soup_requester being deprecated.

Makefile.am

@@ -17,7 +17,8 @@
 
 ACLOCAL_AMFLAGS = -I m4 ${ACLOCAL_FLAGS}
 AM_CPPFLAGS = -DDATADIR='"$(datadir)"' -DLIBEXECDIR='"$(libexecdir)"' \
-	-DGLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_34 -DGLIB_VERSION_MAX_ALLOWED=GLIB_VERSION_2_34
+	-DGLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_34 -DGLIB_VERSION_MAX_ALLOWED=GLIB_VERSION_2_34 \
+	-DSOUP_VERSION_MIN_REQUIRED=SOUP_VERSION_2_40 -DSOUP_VERSION_MAX_ALLOWED=SOUP_VERSION_40
 AM_CFLAGS = $(WARN_CFLAGS)
 
 if BUILD_EMBEDDED_DEPENDENCIES