fake.rb.in: expand srcdir

* template/fake.rb.in (top_srcdir): expand for the case @srcdir@
  is not a relative path.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49945 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

template/fake.rb.in

@@ -22,7 +22,7 @@ class Object
   RUBY_DESCRIPTION = "ruby #{RUBY_VERSION}#{patchlevel_str} (#{RUBY_RELEASE_DATE}) [#{RUBY_PLATFORM}]"
 end
 builddir = File.dirname(__FILE__)
-top_srcdir = File.join(builddir, "@srcdir@")
+top_srcdir = File.expand_path("@srcdir@", builddir)
 $:.unshift(File.expand_path(builddir))
 fake = File.join(top_srcdir, "tool/fake.rb")
 eval(File.read(fake), nil, fake)