[gn] Support dots in CMake paths in the sync script

Some file paths use dots to pick up sources from parent directories.

Differential Revision: https://reviews.llvm.org/D60734

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358774 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed