mkconfig.rb: fix empty prefix

* tool/mkconfig.rb: fix empty RbConfig::CONFIG["prefix"] when
  configured --with-rubyarchprefix, remove prefix from rubyarchdir
  after expansion for the case it does not start with '$(prefix)'.
  [fix GH-643]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46586 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,10 @@
+Sat Jun 28 00:35:10 2014  Lauri Tirkkonen  <lotheac@iki.fi>
+
+	* tool/mkconfig.rb: fix empty RbConfig::CONFIG["prefix"] when
+	  configured --with-rubyarchprefix, remove prefix from rubyarchdir
+	  after expansion for the case it does not start with '$(prefix)'.
+	  [fix GH-643]
+
 Fri Jun 27 15:20:12 2014  SHIBATA Hiroshi  <shibata.hiroshi@gmail.com>
 
 	* lib/rubygems/test_case.rb: rescue Gem::LoadError in Gem::TestCase.

tool/mkconfig.rb

@@ -167,10 +167,10 @@ def vars.expand(val, config = self)
   val.replace(newval) unless newval == val
   val
 end
-vars["prefix"] = ""
-vars["exec_prefix"] = ""
-prefix = vars.expand(vars["rubyarchdir"])
-print "  TOPDIR = File.dirname(__FILE__).chomp!(#{prefix.dump})\n"
+prefix = vars.expand(vars["prefix"])
+rubyarchdir = vars.expand(vars["rubyarchdir"])
+relative_archdir = rubyarchdir.rindex(prefix, 0) ? rubyarchdir[prefix.size..-1] : rubyarchdir
+print "  TOPDIR = File.dirname(__FILE__).chomp!(#{relative_archdir.dump})\n"
 print "  DESTDIR = ", (drive ? "TOPDIR && TOPDIR[/\\A[a-z]:/i] || " : ""), "'' unless defined? DESTDIR\n"
 print <<'ARCH' if universal
   arch_flag = ENV['ARCHFLAGS'] || ((e = ENV['RC_ARCHS']) && e.split.uniq.map {|a| "-arch #{a}"}.join(' '))