Problem:
Build fails without git or .git/.
ref #19289
Solution:
Fix the version generation logic.
Test cases:
If `git` is missing:
-- Using NVIM_VERSION_MEDIUM: v0.8.0-dev
If `.git/` is missing:
-- Git tag extraction failed:
fatal: not a git repository (or any of the parent directories): .git
-- Using NVIM_VERSION_MEDIUM: v0.8.0-dev
If `git describe` fails
-- Git tag extraction failed:
fatal: ...
-- Using NVIM_VERSION_MEDIUM: v0.8.0-dev
Co-authored-by: Justin M. Keyes <justinkz@gmail.com>