Workaround to avoid generic lowering breaking branches.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/520643002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23521 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Properly separate host and target builds when using external natives.

R=rmcilroy@chromium.org, vogelheim@chromium.org

Review URL: https://codereview.chromium.org/506983002

Patch from André Baixo <baixo@google.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23522 ce2b1a6d-e550-0410-aec6-3dcde31c8c00