[cmake] Build libxml from source in release (#221365)
With 23.x we started linking a static libxml in release builds to avoid
requiring that to be installed, and the varying names of that library on
different linux distros. That broke more than it fixed because the
static libxml in our docker images are built targeting ICU, and ICU's
shared library version changes quickly, so even between 2 ubuntu
versions the binaries will not work.
With this change we now build from source in the release build, which is
already what windows does, and we disable ICU / iconv since those don't
seem vital for the windows manifest use case. This seems easier than
building a libxml out of band in our CI images that do the release
builds.
Fixes https://github.com/llvm/llvm-project/issues/215764
Assisted-By: codex
