ruby: fix build of ruby-native with gcc7

Marsalling is broken when ruby-2.2.x is built with gcc7, backport the change
fix  in Ruby SVN r57410 to apply to ruby 2.2.5:

https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=57410

Fixes [YOCTO #12271]

(From OE-Core rev: b9de98cdc816904583970369848181c2c79f1dc5)

Signed-off-by: Joshua Lock <joshua.g.lock@intel.com>
Signed-off-by: Armin Kuster <akuster808@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/ruby/ruby/prevent-gc.patch

@@ -0,0 +1,32 @@
+Fix marshaling with gcc7. Based on upstream revision 57410:
+https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=57410
+https://github.com/ruby/ruby/commit/7c1b30a602ab109d8d5388d7dfb3c5b180ba24e1
+https://bugs.ruby-lang.org/issues/13150
+
+with the upstream patches intent ported to Ruby 2.2.5
+
+Upstream-Status: Backport
+
+Signed-off-by: Joshua Lock <joshua.g.lock@intel.com>
+
+Index: ruby-2.2.5/marshal.c
+===================================================================
+--- ruby-2.2.5.orig/marshal.c
++++ ruby-2.2.5/marshal.c
+@@ -17,7 +17,6 @@
+ #include "ruby/io.h"
+ #include "ruby/st.h"
+ #include "ruby/util.h"
+-
+ #include <math.h>
+ #ifdef HAVE_FLOAT_H
+ #include <float.h>
+@@ -985,7 +984,7 @@ marshal_dump(int argc, VALUE *argv)
+     VALUE obj, port, a1, a2;
+     int limit = -1;
+     struct dump_arg *arg;
+-    VALUE wrapper; /* used to avoid memory leak in case of exception */
++    volatile VALUE wrapper; /* used to avoid memory leak in case of exception */
+ 
+     port = Qnil;
+     rb_scan_args(argc, argv, "12", &obj, &a1, &a2);

meta/recipes-devtools/ruby/ruby_2.2.5.bb

@@ -3,6 +3,8 @@ require ruby.inc
 SRC_URI[md5sum] = "bd8e349d4fb2c75d90817649674f94be"
 SRC_URI[sha256sum] = "30c4b31697a4ca4ea0c8db8ad30cf45e6690a0f09687e5d483c933c03ca335e3"
 
+SRC_URI += "file://prevent-gc.patch"
+
 # it's unknown to configure script, but then passed to extconf.rb
 # maybe it's not really needed as we're hardcoding the result with
 # 0001-socket-extconf-hardcode-wide-getaddr-info-test-outco.patch