python-native: correct prefix handling for oe-core sysroot layout
Don't try to guess a path based on ${HOST_SYS} since this is not where the
files in the sysroot are likely to be. Instead, just use the "plat_specific"
approach of taking STAGING_INCDIR and knocking off the trailing "/include" for
all cases. This is still evidently suboptimal but does at least seem to give
the correct results.
Signed-off-by: Phil Blundell <philb@gnu.org> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
