Bump libffi from 3.4.3 to 3.4.6

Author: mhashizume

configs/components/libffi.rb

@@ -1,6 +1,6 @@
 component 'libffi' do |pkg, settings, platform|
-  pkg.version '3.4.3'
-  pkg.md5sum 'b57b0ac1d1072681cee9148a417bd2ec'
+  pkg.version '3.4.6'
+  pkg.sha256sum 'b0dea9df23c863a7a50e825440f3ebffabd65df1497108e5d437747843895a4e'
   pkg.url "https://github.com/libffi/libffi/releases/download/v#{pkg.get_version}/#{pkg.get_name}-#{pkg.get_version}.tar.gz"
   pkg.mirror "#{settings[:buildsources_url]}/#{pkg.get_name}-#{pkg.get_version}.tar.gz"