Due to the use of the cross-canadian inherit, TARGET_OS can be reset to
values other than the correct one, leading to generation of the wrong
files.
By expanding REAL_MULTIMACH_TARGET_SYS before the inherit, the correct
OS value is preserved and we generate the right environment files.
[YOCTO #6608]
[YOCTO #6613]
(From OE-Core rev: ae265973c96ff4b8b5580436647fc361490e134c)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>