lib/oe/rootfs: tell intercepts where the native sysroot is
Some intercepts may want to access files in the native sysroot that are not on
$PATH (such as something in $libexecdir) but any use of STAGING_DIR_NATIVE in
the postinst that calls the intercept will be "baked" into the package, so if
sstate is reused it will use paths that may not exist.
Solve this by exporting the location of the native sysroot in the environment so
the postinst and intercept can use an environment variable instead of a bitbake
variable.
Signed-off-by: Ross Burton <ross.burton@intel.com>
