[OE-core] Custom CLASSOVERRIDE and a "sub-sysroot" for JavaScript

[chris.laplante at agilent.com]

> Hmm, removing the stamp-extra-info lines leaves me with errors like these:
> 
> ERROR: mc:mc-name:library-emscripten-1.0+gitAUTOINC+ab6d30c10c-r0 do_packagedata_setscene: The recipe library-emscripten is
> trying to install files into a shared area when those files already exist. Those files and their manifest location are:
>   /home/laplante/yocto/build/tmp-mc-mc-name/pkgdata/mach/library-emscripten
>     (matched in manifest-cortexa9t2hf-neon-library-emscripten.packagedata)
>   /home/laplante/yocto/build/tmp-mc-mc-name/pkgdata/mach/runtime/library-emscripten-staticdev
>     (matched in manifest-cortexa9t2hf-neon-library-emscripten.packagedata)
>   /home/laplante/yocto/build/tmp-mc-mc-name/pkgdata/mach/runtime/library-emscripten-dev
>     (matched in manifest-cortexa9t2hf-neon-library-emscripten.packagedata)
> ...
> 


Actually never mind, I had deleted just tmp and retried, but I had forgotten to delete the tmp-mc-* directories. Deleting all of them and retrying worked. 

Thanks again.
Chris