Windows support

[makslevental]

This PR enables building and running on Windows. In its current form only the lit/ctests are being performed since we still don't have a runner with windows in CI. Will add that in a follow-up.

Note, this PR refactors all the CMake in runtime/src/iree-amd-aie/aie_runtime/CMakeLists.txt not for fun but because having those targets built that deep in the directory structure causes problems on Windows (where path lengths are basically limited to 255 characters¹).

This PR also refactors the dependency on XRT. Again not for fun but because it causes problems on Windows. Specifically we no longer build all of XRT which was adding ~10 minutes to total build time and can't be ccached.

How does XRT cause problems?

Documenting here so for posterity: we need various headers from XRT, but XRT's classes expose too much and therefore we actually have to link their libs at compile time (libxrt_coreutil.so) because we're building an executable/static archive ourselves (and therefore all names have to resolved at compile time). The problem is that at runtime you cannot use the libxrt_coreutil.so you built². So we need to do symbol resolution against libxrt_coreutil at compile time but then not install it. Hence $<BUILD_LOCAL_INTERFACE:xrt_coreutil>³.

EDIT: we now also build boost instead of depending on a system/env install. (why: caused problems on window).

Footnotes

1. Yes, I'm completely serious; ↩

2. Because XRT's architecture looks for those libs (and the driver) in special places (like /opt/xilinx/xrt). ↩

3. See BUILD_LOCAL_INTERFACE. ↩