VS: connect /Y- compiler option with "Not Using Precompiled Headers"

Original header commit v3.10.0-rc1~423^2

The change allows to selectively disable PrecompiledHeaders.
Despite the `$(VCTargetsPath)/1033/cl.xml` contains an empty value for switch,
for effectively turn off setting need to use /Y- option as described on msdn:
https://msdn.microsoft.com/en-us/library/1hy7a92h.aspx