cmd executes commands async when it shouldnt

tested and failed on r73237:

An experiment:
Do never open a file browser before any of these tests or it will bias the result, as explorer filebrowser is using ntobjshex.dll! and will lock it.
Do a fresh install before every of this tests to have the same preconditions.
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test1:
-directly after ros install open cmd
type

regsvr32 /s /u ntobjshex.dll

expected result == observed result == dll gets unregistered
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test2:
-directly after ros install open cmd
type

del C:\reactos\system32\ntobjshex.dll

expected result == observed result == dll gets deleted (not unregistered)
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test3:
-directly after ros install start the following batch-file on desktop (and wait a second before continueing the first pause within):

regsvr32 /s /u ntobjshex.dll

pause

del C:\reactos\system32\ntobjshex.dll

pause

expected result == observed result == dll gets unregistered and deleted
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test4:
-directly after ros install start the following batch-file on desktop:

regsvr32 /s /u ntobjshex.dll

del C:\reactos\system32\ntobjshex.dll

pause

expected result: dll gets unregistered and deleted
observed result: most of the time the dll gets not unregistered but properly deleted - OUCH!
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To make expected result == observed result in test4, the batch has to wait until the regsvr32 command is done before running the del command.
In other words regsvr32 should be blocking.