mutt: needs mmu

Fixes:
http://autobuild.buildroot.net/results/8ce/8ceec55fa8358d8821f2deaf3440f5b06270db6a/

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

package/mutt/Config.in

@@ -1,6 +1,7 @@
 config BR2_PACKAGE_MUTT
 	bool "mutt"
 	depends on BR2_USE_WCHAR
+	depends on BR2_USE_MMU # fork()
 	select BR2_PACKAGE_NCURSES
 	help
 	  Mutt is a sophisticated text-based Mail User Agent (MUA)