[Cmake] Precompiled headers with VC++

[John Biddiscombe]

> >   2 Generate a symbol table name (eg TargetPrecompiledHeaders.csm or
> >whatever MSVC uses)
>
> What is that csm file used for in MSVC ?

Sorry, the csm file is the actual binary precompiled header. For each target
a new binary will be needed and borland uses my_binary_pch_file.csm
extension

under msvc it must be something similar

JB