add gtest version 1.8
add gtest version 1.8

Summary:
needed by a few projects [wangle, mvfst, proxygen]

it's already in lfs
https://www.internalfb.com/intern/diffusion/FBS/browse/master/fbcode/tools/lfs/.lfs-pointers?lines=41

Reviewed By: mzlee

Differential Revision: D23676343

fbshipit-source-id: 0fa04d4224f27e756f683924af0c21ea63a90647

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly