[llvm] [cmake] FindLibXml2: fall back to xmlversion.h when pkg-config has no… (PR #207797)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `lldb-arm-ubuntu` running on `linaro-lldb-arm-ubuntu` while building `llvm` at step 6 "test".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/18/builds/26292

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test) failure: build (failure)
...
PASS: lldb-api :: test_utils/TestInlineTest.py (1295 of 2921)
PASS: lldb-api :: test_utils/TestDecorators.py (1296 of 2921)
PASS: lldb-api :: test_utils/TestPExpectTest.py (1297 of 2921)
PASS: lldb-api :: test_utils/base/TestBaseTest.py (1298 of 2921)
PASS: lldb-api :: test_utils/pdb/TestPdb.py (1299 of 2921)
UNSUPPORTED: lldb-api :: tools/lldb-dap/attach/TestDAP_attach.py (1300 of 2921)
UNSUPPORTED: lldb-api :: tools/lldb-dap/attach/TestDAP_attachByPortNum.py (1301 of 2921)
PASS: lldb-api :: terminal/hidden_frame_markers/TestHiddenFrameMarkers.py (1302 of 2921)
PASS: lldb-api :: tools/lldb-dap/breakpoint-events/TestDAP_breakpointEvents.py (1303 of 2921)
TIMEOUT: lldb-api :: functionalities/scripted_frame_provider/circular_dependency/TestFrameProviderCircularDependency.py (1304 of 2921)
******************** TEST 'lldb-api :: functionalities/scripted_frame_provider/circular_dependency/TestFrameProviderCircularDependency.py' FAILED ********************
Script:
--
/usr/bin/python3.10 /home/tcwg-buildbot/worker/lldb-arm-ubuntu/llvm-project/lldb/test/API/dotest.py -u CXXFLAGS -u CFLAGS --env LLVM_LIBS_DIR=/home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/./lib --env LLVM_INCLUDE_DIR=/home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/include --env LLVM_TOOLS_DIR=/home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/./bin --triple armv8l-unknown-linux-gnueabihf --build-dir /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/lldb-test-build --lldb-module-cache-dir /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/lldb-test-build/module-cache-lldb/lldb-api --clang-module-cache-dir /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/lldb-test-build/module-cache-clang/lldb-api --executable /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/./bin/lldb --lldb-python-dir /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/local/lib/python3.10/dist-packages --compiler /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/./bin/clang --dsymutil /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/./bin/dsymutil --make /usr/bin/gmake --llvm-tools-dir /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/./bin --lldb-obj-root /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/tools/lldb --lldb-libs-dir /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/./lib --cmake-build-type Release /home/tcwg-buildbot/worker/lldb-arm-ubuntu/llvm-project/lldb/test/API/functionalities/scripted_frame_provider/circular_dependency -p TestFrameProviderCircularDependency.py
--
Exit Code: -9
Timeout: Reached timeout of 600 seconds


********************
PASS: lldb-api :: tools/lldb-dap/breakpoint/TestDAP_breakpointLocations.py (1305 of 2921)
PASS: lldb-api :: tools/lldb-dap/breakpoint-assembly/TestDAP_breakpointAssembly.py (1306 of 2921)
PASS: lldb-api :: tools/lldb-dap/breakpoint/TestDAP_setExceptionBreakpoints.py (1307 of 2921)
PASS: lldb-api :: tools/lldb-dap/breakpoint/TestDAP_logpoints.py (1308 of 2921)
PASS: lldb-api :: tools/lldb-dap/breakpoint/TestDAP_setFunctionBreakpoints.py (1309 of 2921)
PASS: lldb-api :: tools/lldb-dap/attach-commands/TestDAP_attachCommands.py (1310 of 2921)
PASS: lldb-api :: tools/lldb-dap/breakpoint/TestDAP_setBreakpoints.py (1311 of 2921)
PASS: lldb-api :: tools/lldb-dap/cancel/TestDAP_cancel.py (1312 of 2921)
PASS: lldb-api :: tools/lldb-dap/commands/TestDAP_commands.py (1313 of 2921)
PASS: lldb-api :: tools/lldb-dap/console/TestDAP_redirection_to_console.py (1314 of 2921)
PASS: lldb-api :: tools/lldb-dap/completions/TestDAP_completions.py (1315 of 2921)
PASS: lldb-api :: tools/lldb-dap/coreFile/TestDAP_coreFile.py (1316 of 2921)
PASS: lldb-api :: tools/lldb-dap/console/TestDAP_console.py (1317 of 2921)
PASS: lldb-api :: tools/lldb-dap/disassemble/TestDAP_disassemble.py (1318 of 2921)
PASS: lldb-api :: tools/lldb-dap/databreakpoint/TestDAP_setDataBreakpoints.py (1319 of 2921)
PASS: lldb-api :: tools/lldb-dap/exception/TestDAP_exception.py (1320 of 2921)
UNSUPPORTED: lldb-api :: tools/lldb-dap/exception/asan/TestDAP_asan.py (1321 of 2921)
PASS: lldb-api :: tools/lldb-dap/disconnect/TestDAP_disconnect.py (1322 of 2921)
UNSUPPORTED: lldb-api :: tools/lldb-dap/exception/objc/TestDAP_exception_objc.py (1323 of 2921)
PASS: lldb-api :: tools/lldb-dap/eventStatistic/TestVSCode_eventStatistic.py (1324 of 2921)
UNSUPPORTED: lldb-api :: tools/lldb-dap/exception/ubsan/TestDAP_ubsan.py (1325 of 2921)
UNSUPPORTED: lldb-api :: tools/lldb-dap/extendedStackTrace/TestDAP_extendedStackTrace.py (1326 of 2921)
PASS: lldb-api :: tools/lldb-dap/exception/cpp/TestDAP_exception_cpp.py (1327 of 2921)
PASS: lldb-api :: tools/lldb-dap/invalidated-event/TestDAP_invalidatedEvent.py (1328 of 2921)
PASS: lldb-api :: tools/lldb-dap/instruction-breakpoint/TestDAP_instruction_breakpoint.py (1329 of 2921)
PASS: lldb-api :: tools/lldb-dap/launch/TestDAP_launch_args.py (1330 of 2921)
PASS: lldb-api :: tools/lldb-dap/launch/TestDAP_launch_basic.py (1331 of 2921)
PASS: lldb-api :: tools/lldb-dap/io/TestDAP_io.py (1332 of 2921)
UNSUPPORTED: lldb-api :: tools/lldb-dap/launch/TestDAP_launch_commands.py (1333 of 2921)

```

</details>

https://github.com/llvm/llvm-project/pull/207797