[gn build] Set +x bit on .py files in llvm/utils/gn/build.

Also add a shebang line to write_cmake_config.py.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@347928 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed