libcurl: needs MMU

Fixes
http://autobuild.buildroot.org/results/5a502f16ad94a410ca21c9a7f223d6c12086bbb5/build-end.log

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/libcurl/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_LIBCURL
 	bool "libcurl"
+	depends on BR2_USE_MMU # Uses fork()
 	help
 	  cURL is a tool for getting files from FTP, HTTP, Gopher, Telnet,
 	  and Dict servers, using any of the supported protocols.