Ensure builtin binaries are aligned to ibf_header

Since IBF result string size should be multiple of 4, this should not
increase the binary size actually.

Author: nobu

template/builtin_binary.inc.tmpl

@@ -5,19 +5,24 @@
 % unless ARGV.include?('--cross=yes')
 %   ary = RubyVM.enum_for(:each_builtin).to_a
 %   ary.each{|feature, iseq|
+%     bin = iseq.to_binary
 
-static const unsigned char <%= feature %>_bin[] = {
-%     iseq                   \
-%     . to_binary            \
+static const union {
+    unsigned char binary[<%= bin.bytesize %>];
+    uint32_t align_as_ibf_header;
+} <%= feature %>_builtin = {
+    .binary = {
+%     bin                    \
 %     . each_byte            \
 %     . each_slice(12) {|a|
-    <%= a.map{ '0x%02x,' % _1 }.join(' ') %>
+        <%= a.map{ '0x%02x,' % _1 }.join(' ') %>
 %     }
+    }
 };
 %   }
 
 #define BUILTIN_BIN(feature) \
-    { #feature, feature ## _bin, sizeof(feature ## _bin), }
+    { #feature, feature ## _builtin.binary, sizeof(feature ## _builtin.binary), }
 static const struct builtin_binary builtin_binary[] = {
 %   ary.each{|feature, |
     BUILTIN_BIN(<%= feature %>),