🍒 [lldb] Add build option to specify the libxml 2 version (llvm#142183)

[Steelskin]

The Swift Windows toolchain uses its own static build of libxml 2, which is more recent than 2.8, resulting in the provided libxml 2 to be rejected. This change allows to specify a custom version for libxml 2, while defaulting to 2.8.

(cherry-picked from commit llvm/llvm-project@a080c74)

[JDevlieghere]

@swift-ci test

[compnerd]

18:05:42  Traceback (most recent call last):
18:05:42    File "C:\Users\swift-ci\jenkins\workspace\apple-llvm-project-pull-request-windows\swift\utils\line-directive", line 738, in <module>
18:05:42      run()
18:05:42    File "C:\Users\swift-ci\jenkins\workspace\apple-llvm-project-pull-request-windows\swift\utils\line-directive", line 689, in run
18:05:42      command = subprocess.Popen(
18:05:42    File "C:\Program Files (x86)\Microsoft Visual Studio\Shared\Python39_64\lib\subprocess.py", line 951, in __init__
18:05:42      self._execute_child(args, executable, preexec_fn, close_fds,
18:05:42    File "C:\Program Files (x86)\Microsoft Visual Studio\Shared\Python39_64\lib\subprocess.py", line 1420, in _execute_child
18:05:42      hp, ht, pid, tid = _winapi.CreateProcess(executable, args,
18:05:42  FileNotFoundError: [WinError 206] The filename or extension is too long
18:05:42  Batch file failed at line 6 with errorcode 1

[compnerd]

@swift-ci please test Windows platform

[compnerd]

@swift-ci please test

[compnerd]

Please test with following PRs:
swiftlang/swift#81961

@swift-ci please test Windows platform

[Steelskin]

The line-directive issue should be fixed with swiftlang/swift#81996

[compnerd]

@swift-ci please test macOS platform

[compnerd]

@swift-ci please test Windows platform

[compnerd]

@swift-ci please test Windows platform

[compnerd]

@swift-ci please test macOS platform