Allow using system pugixml for build about r2ghidra HOT 4 OPEN

Using subproject wraps this is actually really easy and Meson provides all the tools and UX for making this an option without you doing anything. Just, in addition to the above patch, create the directory subprojects/ and run meson wrap install pugixml.

from r2ghidra.

What i find out is that the pugixml dependency doesnt work even if it builds it fails at runtime because the apis changed (thats why its not using the last version of pugixml). Ideally i would prefer to depend on r2's xml parser instead. So we dont depend on external things that eventually break

so im not a big fan of adding the pption to use system wide pugixml

from r2ghidra.

Just add an exact version of pugixml as a dependency. If the system version is too new, it will not be found and the bundled one is forced.

from r2ghidra.

To me that looks like an extra moving piece that makes the maintainance harder and opens the doors to new bugs. But if thats not enabled by default and distros are happy with it im fine to ship it as a temporal fix. But the proper fix would be to use r2xml instead of external code

from r2ghidra.