devel/llvm20: Link LLDB with libxml2 to allow an interop with openocd

[arrowd]

Summary

I got a report that LLDB may silently grap the libxml2 dependency if
it is installed on the building machine. Linking to libxml2 allows it to
interoperate with openocd and parse XML register descriptions.

This patch makes libxml2 a dependency if the LLDB is enabled

Test Plan

poud testport and ldd /usr/local/llvm20/bin/lldb | grep libxml

[brooks]

Thanks for the report. This works by accident as a later LLDB_USES squashes gnome, but clang adds it and then doesn't actually use it... I'm working on an alternate fix along with a bump of the lua version.

[arrowd]

The issue is still there, so I'm updating the diff, just in case

[brooks]

Sorry for the delay, I've been traveling too much over the last couple weeks and am finally tuning back in. I've got a tested patch, but want to push an update to 20.1.7 along with this change to reduce the number of rebuilds globally. The build is in progress and I'll hopefully push in the next 24 hours.