Don't use anonymous types declared in an anonymous union.

They are a non-standard extension (probably in C1X, IIRC), but clang is unhappy
with them when -Wnested-anon-types is enabled, which seems to be implied by
-pedantic.

With this change and the previous fix for clang, we are now -Werror clean, even
on clang 3.3.

R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/14850016

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14659 ce2b1a6d-e550-0410-aec6-3dcde31c8c00