Automerge: [bazel] Add support for multiple tblgen outputs (#168158)

Required after llvm/llvm-project#167700

This adds yet another format for `tbl_outs` where you pass the list of
opts, and a list of outputs (where previously you could only have 1
output). In that case all outputs must be produced, but the first is
used for the `-o` arg since tblgen is generating the other names based
on that single argument.

Author: keith