[CMake] Compilation speed with CMake/NMake combination, making it faster?

[Sylvain Benner]

>> *         We're using an NMake build tree, is NMake particularly
>> slow?  Do any of the other makes work more efficiently?
>>     
>
> Be aware that nmake builds are much slower than using devenv, as nmake starts a cl.exe process for every single file,
> whereas devenv calls cl.exe with several source files. This costs, due to the high process overhead on Windows
Maybe using compilation units might help.With devenv, we get up to x9 
faster compilation time using them (usually only one or two compilation 
units for each project).

--Sylvain