* common.mk (yes-btest): btest depends on also $(arch)-fake.rb and
  rbconfig.rb on building for NativeClient.

* Makefile.in (fake): Avoid generating $(arch)-fake.rb unless cross
  compiling.

* configure.in (CROSS_COMPILING): New substitution.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38692 b2dd03c8-39d4-4d8f-98ff-823fe69b080e