gn build: Add a resource_dir.gni file.

The path to the resource directory will end up being used in several
more places once the support for running check-hwasan lands. This
moves the definition to a central location so that it can be used
from those places.

Differential Revision: https://reviews.llvm.org/D56700

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@351255 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed