Revert "Set host_arch to ia32 on machines with a 32bit userland but a 64bit kernel."

This reverts r21909.

Reason: breaks NaCL build.

BUG=
TBR=jochen@chromium.org

Review URL: https://codereview.chromium.org/346223004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21914 ce2b1a6d-e550-0410-aec6-3dcde31c8c00