build: gracefully handle error in git-version #19289

- only update git-version if both of these conditions are met:
    - `git` command succeeds
    - `versiondef_git.h` would change (SHA1-diff)
- else print a status/warning message

also move version generation out of Lua into cmake.

scripts/update_version_stamp.lua

@@ -1,54 +0,0 @@
-#!/usr/bin/env lua
---
--- Script to update the Git version stamp during build.
--- This is called via the custom update_version_stamp target in
--- src/nvim/CMakeLists.txt.
---
--- arg[1]: file in which to update the version string
--- arg[2]: prefix to use always ("vX.Y.Z")
-
-local function die(msg)
-  io.stderr:write(string.format('%s: %s\n', arg[0], msg))
-  -- No error, fall back to using generated "-dev" version.
-  os.exit(0)
-end
-
-local function iswin()
-  return package.config:sub(1,1) == '\\'
-end
-
-if #arg ~= 2 then
-  die(string.format("Expected two args, got %d", #arg))
-end
-
-local versiondeffile = arg[1]
-local prefix = arg[2]
-
-local dev_null = iswin() and 'NUL' or '/dev/null'
-local described = io.popen('git describe --first-parent --dirty 2>'..dev_null):read('*l')
-if not described then
-  described = io.popen('git describe --first-parent --tags --always --dirty'):read('*l')
-end
-if not described then
-  io.open(versiondeffile, 'w'):write('\n')
-  die('git-describe failed, using empty include file.')
-end
-
--- `git describe` annotates the most recent tagged release; for pre-release
--- builds we append that to the dev version
-local with_prefix = prefix
-if prefix:match('-dev$') ~= nil then
-  with_prefix = prefix .. '+' .. described:gsub('^v%d+%.%d+%.%d+-', '')
-end
-
--- Read existing include file.
-local current = io.open(versiondeffile, 'r')
-if current then
-  current = current:read('*l')
-end
-
--- Write new include file, if different.
-local new = '#define NVIM_VERSION_MEDIUM "'..with_prefix..'"'
-if current ~= new then
-  io.open(versiondeffile, 'w'):write(new .. '\n')
-end