Issue #17743: Now use extended syntax of set command in .bat files.

Lib/venv/scripts/nt/activate.bat

 @echo off
-set VIRTUAL_ENV=__VENV_DIR__
+set "VIRTUAL_ENV=__VENV_DIR__"
 
 if not defined PROMPT (
-    set PROMPT=$P$G
+    set "PROMPT=$P$G"
 )
 
 if defined _OLD_VIRTUAL_PROMPT (
-    set PROMPT=%_OLD_VIRTUAL_PROMPT%
+    set "PROMPT=%_OLD_VIRTUAL_PROMPT%"
 )
 
 if defined _OLD_VIRTUAL_PYTHONHOME (
-     set PYTHONHOME=%_OLD_VIRTUAL_PYTHONHOME%
+    set "PYTHONHOME=%_OLD_VIRTUAL_PYTHONHOME%"
 )
 
-set _OLD_VIRTUAL_PROMPT=%PROMPT%
-set PROMPT=__VENV_NAME__%PROMPT%
+set "_OLD_VIRTUAL_PROMPT=%PROMPT%"
+set "PROMPT=__VENV_NAME__%PROMPT%"
 
 if defined PYTHONHOME (
-     set _OLD_VIRTUAL_PYTHONHOME=%PYTHONHOME%
+    set "_OLD_VIRTUAL_PYTHONHOME=%PYTHONHOME%"
     set PYTHONHOME=
 )
 
-if defined _OLD_VIRTUAL_PATH set PATH=%_OLD_VIRTUAL_PATH%; goto SKIPPATH
-
-set _OLD_VIRTUAL_PATH=%PATH%
+if defined _OLD_VIRTUAL_PATH (
+    set "PATH=%_OLD_VIRTUAL_PATH%"
+) else (
+    set "_OLD_VIRTUAL_PATH=%PATH%"
+)
 
-:SKIPPATH
-set PATH=%VIRTUAL_ENV%\__VENV_BIN_NAME__;%PATH%
+set "PATH=%VIRTUAL_ENV%\__VENV_BIN_NAME__;%PATH%"
 
 :END