try to git-add src/test/buildenv.py . the command should add rise an error along with a message similar to this one:
The following paths are ignored by one of your .gitignore files:
Use -f if you really want to add them.
It is generated by make check and it's an helper file that contains the extension to be used for binaries aiding the execution of the unit tests. When you run on Linux it's content is something like:
whereas when you're cross compiling for win32/64:
I've never seen this file. My build generates test/config.ini which is read by the test harness. I'm fairly sure this is legacy -- we backported a commit a long time ago related to this.