Windows installer does not ship UDUNITS XML files

[slayoo]

CC: @pjb7687, @jdtreffert, @GillesDuvert, @acoulais

reported here: https://github.com/gnudatalanguage/gdl/discussions/1723

the installer does not ship XML definition files which are needed to use UDUNITS routines.

errors happen at runtime, e.g. when trying to use IMSL_CONSTANT

things that are needed to be done:

• include these XML files with the installer
• add CI test logic that would be running GDL unit tests with the installer-installed GDL

[GillesDuvert]

somebody with Windows pls. provide the windows path for this or these files.