Fuchsia has always been using ABI version 2 but I forgot this option
when setting up the cache file for runtimes build.

Differential Revision: https://reviews.llvm.org/D35705

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@308705 91177308-0d34-0410-b5e6-96231b3b80d8