perl: needs MMU

see build http://autobuild.buildroot.net/results/ba7/ba71d0d532ccd8e16b727cddd5dcaa5521074945/

Signed-off-by: Francois Perrad <francois.perrad@gadz.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/perl/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_PERL
 	bool "perl"
+	depends on BR2_USE_MMU # fork()
 	help
 	  Larry Wall's Practical Extraction and Report Language
 	  An interpreted scripting language, known among some as "Unix's Swiss