The new feature in GitHub called 'GitHub Codespaces' generates a
pythonenv3.8 directory in the root level of the llvm-project git
checkout. So I am adding that directory to the .gitignore.
See the following for more info:
https://github.com/features/codespaces
Differential Revision: https://reviews.llvm.org/D86846
# VS2017 and VSCode config files.
.vscode
.vs
+# pythonenv for github Codespaces
+pythonenv*
# clangd index. (".clangd" is a config file now, thus trailing slash)
.clangd/
.cache