USE_SPGLIB only installs header file without USE_QT, and also installs SpaceGroup.a with USE_QT

[yurivict]

Avogadro version: (please complete the following information from the About box):

• Avogadrolibs: 1.94.0
• Qt: 5.15.2

Desktop version: (please complete the following information):

• OS: FreeBSD
• Compiler: clang-11

Describe the bug
The header include/avogadro/core/avospglib.h and the corresponding library lib/avogadro2/staticplugins/SpaceGroup.a should be installed together. Currently USE_SPGLIB only enables the header, and then USE_QT enables the library.
If Qt is required for USE_SPGLIB it should break and say so when USE_SPGLIB=ON USE_QT=OFF

[ghutchis]

No, I think this is the correct behavior. The SpaceGroup.a is the Qt-based plugin for the GUI. The header can be used, e.g, by the Jupyter Python code. Right now, it doesn't use spacegroup.h but it will. The underlying non-Qt code uses spglib and doesn't need SpaceGroup.a