ARM7EJ-S doesn't present in ARM.td

May I submit a patch about this?

There isn't anything stopping you posting a patch, see
https://llvm.org/docs/DeveloperPolicy.html . Finding a willing
reviewer might be more challenging as it isn't as simple as just
adding a line to ARM.td, existing tests may need to be updated, and
tests that cover the selection of arm7ej-s will need adding. If you
are just wanting to generate code for the cpu I recommend using
-march=armvte

Peter