ruby: fix verconf.h related build failure

See [1] for failure analysis.

Fixes:
   http://autobuild.buildroot.net/results/c94fef5d2cfb00a336905ae3c110d7680f6d5416/
   http://autobuild.buildroot.net/results/4375cb1e325a336dbf59f22f975be9165ad0648a/

[1] http://lists.busybox.net/pipermail/buildroot/2014-December/114273.html

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/ruby/ruby.mk

@@ -64,6 +64,13 @@ else
 	RUBY_CONF_OPTS += --without-gmp
 endif
 
+# workaround for amazing build failure, see
+# http://lists.busybox.net/pipermail/buildroot/2014-December/114273.html
+define RUBY_REMOVE_VERCONF_H
+	rm -f $(@D)/verconf.h
+endef
+RUBY_POST_CONFIGURE_HOOKS += RUBY_REMOVE_VERCONF_H
+
 # Remove rubygems and friends, as they need extensions that aren't
 # built and a target compiler.
 RUBY_EXTENSIONS_REMOVE = rake* rdoc* rubygems*