Add --cmake-toolchain and --remote-host flags for test-suite

[lukel97]

When cross-compiling LLVM test-suite to run on another machine, you usually need to pass a toolchain file and -DTEST_SUITE_REMOTE_HOST to CMake.

This adds two flags to the CLI to make it more convenient to configure these (as opposed to passing in -DCMAKE_TOOLCHAIN_FILE/-DTEST_SUITE_REMOTE_HOST)

[DavidSpickett]

I rarely use LNT but I assume there is a way to pass these options but it's something like:

lnt --extra-cmake-stuff "A=B;C=D"

Which is a bit free form and more guess work of what to pass?

[lukel97]

I rarely use LNT but I assume there is a way to pass these options but it's something like:

lnt --extra-cmake-stuff "A=B;C=D"

Which is a bit free form and more guess work of what to pass?

Yup, all this is a more explicit way of writing lnt runtest test-suite -DTEST_SUITE_REMOTE_HOST=... -DCMAKE_TOOLCHAIN_FILE=.... I figured having the explicit CLI makes it more discoverable and acts as a bit of documentation. We have other arguments like --cc, --cflags, --benchmarking-only that do the same thing and just forward CMake variables.

[DavidSpickett]

In some sense a CMake toolchain file is also a nicer, discoverable way, to pass a bunch of random things you can use normal options for. Same motivations.

So this LGTM.

I'd say wait for someone else to approve but we don't have many reviewers here in LNT. Wait it a day or two in case anyone else wants to comment, otherwise go ahead with this.