libev: also fails for blackfin

Also fails for blackfin because of a lack of memory fences so disable
it. Fixes:
http://autobuild.buildroot.net/results/d895f0b0a5f4b6c173c2843a76277e6fe611627b/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/libev/Config.in

@@ -1,7 +1,7 @@
 config BR2_PACKAGE_LIBEV
 	bool "libev"
 	# needs memory fences
-	depends on !BR2_avr32
+	depends on !(BR2_avr32 || BR2_bfin)
 	help
 	  Userspace library for handling asynchronous notifications