XMLElements: fix tinyxml include

[andresailer]

BEGINRELEASENOTES

• XMLElements: fix build when not using XercesC, failing to include header files

ENDRELEASENOTES

[github-actions[bot]]

Test Results

   14 files     14 suites   6h 47m 57s :stopwatch:   363 tests   363 :white_check_mark: 0 :zzz: 0 :x: 2 496 runs  2 496 :white_check_mark: 0 :zzz: 0 :x:

Results for commit 16113ee2.