[CMake] Native Pathsupport under Windows

[alexander at camek.de]

Hi all,
Hi Brandon,

>You'll need to write your own native path function for MinGW generator
>as a workaround.  STRING(REPLACE "/" "\\" native_path "${cmake_path}")
>will probably do it, but maybe there's more to it.  It's been awhile
>since I messed with these.

Works great, now i can do a native append.

Thanks for your help.

Greetings

Alexander