[OE-core] [PATCH] cmake: add CMAKE_SYSROOT to generated toolchain file

[Bach, Pascal]

> > Fixes problems which we have also seen on sumo branch. Thanks for this!
> 
> Sorry, spoke too soon. This fixes compilation on a few recipes in my tree but
> there are still lots failures with the same error message. We had a hacky
> patch to cmake as a workaround but that too causes some problems:

I have not yet figured out what CMake based projects are affected and why.
The error seems to happen only for certain projects.

> --- a/Modules/Compiler/GNU.cmake
> +++ b/Modules/Compiler/GNU.cmake
> @@ -45,7 +45,7 @@
>    set(CMAKE_${lang}_CREATE_PREPROCESSED_SOURCE
> "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -E
> <SOURCE> > <PREPROCESSED_SOURCE>")
>    set(CMAKE_${lang}_CREATE_ASSEMBLY_SOURCE
> "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -S
> <SOURCE> -o <ASSEMBLY_SOURCE>")
>    if(NOT APPLE OR NOT CMAKE_${lang}_COMPILER_VERSION VERSION_LESS
> 4) # work around #4462
> -    set(CMAKE_INCLUDE_SYSTEM_FLAG_${lang} "-isystem ")
> +    set(CMAKE_INCLUDE_SYSTEM_FLAG_${lang} "-I ")
>    endif()
> 
>    set(_CMAKE_${lang}_IPO_SUPPORTED_BY_CMAKE YES)
> 
> I wonder what the real fix could be...
> 

This looks similar to another workaround I saw.
Setting CMAKE_NO_SYSTEM_FROM_IMPORTED to True. I'm also not sure what the real fix is.
The issue is also discussed here: https://gitlab.kitware.com/cmake/cmake/issues/16291

Pascal