build,windows: restore DISTTYPEDIR

* rename :exit to :distexit

PR-URL: https://github.com/nodejs/node/pull/13969
Refs: https://github.com/nodejs/node/pull/13900#pullrequestreview-46906389
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: João Reis <reis@janeasystems.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Rod Vagg <rod@vagg.org>

vcbuild.bat

@@ -534,7 +534,7 @@ if not defined NODE_VERSION (
 if not defined DISTTYPE set DISTTYPE=release
 if "%DISTTYPE%"=="release" (
   set FULLVERSION=%NODE_VERSION%
-  exit /b 0
+  goto distexit
 )
 if "%DISTTYPE%"=="custom" (
   if not defined CUSTOMTAG (
@@ -561,4 +561,7 @@ if not "%DISTTYPE%"=="custom" (
   set TAG=%DISTTYPE%%DATESTRING%%COMMIT%
 )
 set FULLVERSION=%NODE_VERSION%-%TAG%
-exit /b 0
+
+:distexit
+if not defined DISTTYPEDIR set DISTTYPEDIR=%DISTTYPE%
+goto :EOF