lib/mkmf.rb: sort list of object files in generated Makefile

Without sorting the list explicitely, its order is indeterministic,
because readdir() is also not deterministic.
When the list of object files varies between builds, they are linked
in a different order, which results in an unreproducible build.

Author: reinerh

debian/changelog

@@ -14,6 +14,8 @@ ruby2.3 (2.3.1-2) UNRELEASED; urgency=medium
     (Closes: #822072)
   * Raise priority to "optional", now that ruby2.2 is gone, although
     the value of this change is unclear. (Closes: #822911)
+  * Apply patch from Reiner Herrmann <[email protected]> to help with
+    reproducibility of mkmf.rb using packages. (Closes: #825569)
 
  -- Antonio Terceiro <[email protected]>  Thu, 28 Apr 2016 09:33:58 -0300
 

lib/mkmf.rb

@@ -2275,7 +2275,7 @@ def create_makefile(target, srcprefix = nil)
 LIBS = #{$LIBRUBYARG} #{$libs} #{$LIBS}
 ORIG_SRCS = #{orig_srcs.collect(&File.method(:basename)).join(' ')}
 SRCS = $(ORIG_SRCS) #{(srcs - orig_srcs).collect(&File.method(:basename)).join(' ')}
-OBJS = #{$objs.join(" ")}
+OBJS = #{$objs.sort.join(" ")}
 HDRS = #{hdrs.map{|h| '$(srcdir)/' + File.basename(h)}.join(' ')}
 TARGET = #{target}
 TARGET_NAME = #{target && target[/\A\w+/]}