Enable `-mllvm -verify-machineinstrs` option by default

[atrosinenko]

Initially, it was proposed to enable -mllvm -verify-machineinstrs option by default in #15:

This option is useful for testing, but it would fail the build unless the LLVM_BRANCH specified includes llvm/llvm-project@22968f5, thus I marked this PR as a draft until we update the default branches as well.

Unfortunately, it turned out other changes to the backend made this check fail even with llvm/llvm-project@22968f5. As #15 introduces other important changes, I would rather investigate this failure in the background and unblock #15.