Fix typo in header guard of v8-platform.h

TBR=svenpanne@chromium.org
BUG=none
LOG=n

Review URL: https://codereview.chromium.org/76313002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17879 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Remove faulty CHECK() statement.

TBR=svenpanne@chromium.org
BUG=none
LOG=n

Review URL: https://codereview.chromium.org/67463003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17880 ce2b1a6d-e550-0410-aec6-3dcde31c8c00