Strictly speaking NAN from math.h is not in a POSIX standard but in C99. However it seems that all our POSIX platforms have it.
Review URL: http://codereview.chromium.org/464015

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3405 ce2b1a6d-e550-0410-aec6-3dcde31c8c00