Updated Win32 genversion.bat to generate version.mk if Git is found, use it if...

Updated Win32 genversion.bat to generate version.mk if Git is found, use it if it isn't, and produce unknown version and leave it untouched if it isn't already found

win32/genversion.bat

 @echo off
 
+setlocal enableextensions enabledelayedexpansion
+
 for /f %%v in ('git describe --tags --match "v*"') do set version=%%v
 
+if not "%version%"=="" goto :gotversion
+
+if exist "%~dp0..\version.mk" goto :getversion
+
+echo Git cannot be found, nor can version.mk. Generating unknown version.
+
+set version=unknown
+
+goto :gotversion
+
+:getversion
+
+for /f "delims== tokens=2" %%v in (%~dp0..\version.mk) do set version=%%v
+
+set version=!version:^"=!
+set version=!version: =!
+
+:gotversion
+
 set version_out=#define %2 "%version%"
+set version_mk=%2 = "%version%"
+
+echo %version_out%> %1_temp
+
+if %version%==unknown goto :skipgenerate
+
+echo %version_mk%> "%~dp0..\version.mk"
 
-echo %version_out% > %1_temp
+:skipgenerate
 
 echo n | comp %1_temp %1 > NUL 2> NUL