The build summary is meant to reflect key configuration variables. Information
about the build system we're running on is important but currently missing
from the information displayed.
Printing TARGET_SYS removes the need to print TARGET_OS and TARGET_ARCH
and we add BUILD_SYS and NATIVELSBSTRING to show information about the
build system.
[YOCTO #3456]
(From OE-Core rev: 764cc1eb3043c84121f597d2271108b91052095e)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>