build: search 'legacy' at line start in build.sdv.config
For modern SDV the build.sdv.config file may contain
'no legacy' or '-legacy'.
@@ -188,7 +188,7 @@ echo Set SDV mode to LEGACY
set SDVLEGACY=1
if not exist "%~dp1\build.sdv.config" goto :eof
echo Checking SDV configuration for %1
-findstr /i legacy "%~dp1\build.sdv.config"
+findstr /b /i legacy "%~dp1\build.sdv.config"
IF NOT ERRORLEVEL 1 goto :eof
echo Using MODERN SDV mode
set SDVLEGACY=
