3-component triple *-none-* is incorrectly normalized to *-none-unknown-* instead of *-unknown-none-*

[wzssyqa]

$ clang --target=aarch64-none-elf --print-target-triple
aarch64-none-unknown-elf
$ clang --target=armv7m-none-eabi --print-target-triple
armv7m-none-unknown-eabi

The expected value is that none and unknown should be swapped.
Caused by std::string Triple::normalize(StringRef Str) in llvm/lib/TargetParser/Triple.cpp.

[wzssyqa]

@peterwaller-arm

[peterwaller-arm]

Is the title of this ticket correct? The issue is that Vendor=none and OS=unknown when triples for example aarch64-none-elf go through normalization, where I believe we expect Vendor=unknown and OS=none.