ifchange.bat: --keep option

* win32/ifchange.bat: add --keep option as well as tool/ifchange.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43309 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

win32/ifchange.bat

@@ -2,6 +2,7 @@
 :: usage: ifchange target temporary
 
 set timestamp=
+set keepsuffix=
 :optloop
 for %%I in (%1) do set opt=%%~I
 if "%opt%" == "--timestamp" (
@@ -12,6 +13,14 @@ if "%opt%" == "--timestamp" (
     set timestamp=%opt:~12%
     shift
     goto :optloop
+) else if "%opt%" == "--keep" (
+    set keepsuffix=.old
+    shift
+    goto :optloop
+) else if "%opt:~0,7%" == "--keep=" (
+    set keepsuffix=%opt:~7%
+    shift
+    goto :optloop
 )
 if "%opt%" == "" goto :end
 
@@ -51,6 +60,7 @@ echo assuming %1 should be changed.
 echo %1 updated.
 :: if exist %1 del %1
 dir /b %2
+if "%keepsuffix%" != "" %1 %1%keepsuffix%
 copy %2 %1
 del %2
 goto :end