[poky] --with-gxx-include-dir and sysroot

[Khem Raj]

> I really don't think its this simple.
>
> Looking at the gcc code, I propose we patch cppdefault.c so instead of
>
> GPLUSPLUS_INCLUDE_DIR "G++", 1, 1, 0, 0
>
> is says
>
> GPLUSPLUS_INCLUDE_DIR "G++", 1, 1, 1, 0

This looks ok fix if you take care of doing it only for case
when sysroot is set and its cross compiling.Although I wonder
if this will also alter the install location of the headers