1.40.0 release

New features:
- tuxmake: accept Kbuild targets as positional arguments
- tuxmake: accept kconfig targets as positional arguments

Bug fixes:
- kselftest: pass KDIR to enable out-of-tree module builds
- kselftest: allow partial build failures
- target: accept any CONFIG_*=<value> inline fragment
- kselftest: report WARNING status on nonfatal failures
- kselftest: use make -i for the install step
- docs: update --kconfig-add help text, remove kselftest-merge target

Container images:
- arch: unify sh, sh2 and sh4 into a single sh architecture
- Update korg-clang-22 to 22.1.4