CMake warnings from snap build must be reduced

[furgo16]

The CMake configuration step while building the current snap package produces a significant number of different warnings, which are not otherwise present in a regular build. They must be addressed individually and the cause of the warning be removed where possible. The goal is to reduce the signal to noise ratio in the log outputs and to avoid underlying issues that might not affect the build, but might surface later unexpectedly. This is such an example: #157

This master issue contains a task list that breaks down the different types of warnings into an actionable issue for each:

• CMake warnings: Policy CMP0175 is not set #165 (333 warnings)
• CMake warning: files in some directories may conflict with libraries in implicit directories #160 (65 warnings)
• CMake warning: The imported target "vtkParseOGLExt" references the file "/usr/bin/vtkParseOGLExt-7.1" but this file does not exist. #163 (4 warnings)
• CMake warning: Policy CMP0167 is not set #164 (1 warning)

[furgo16]

Most tasks on this issue were already fixed by FreeCAD/FreeCAD#19725. I think it makes sense to close this issue now and leave the remaining open task as a standalone issue, which is snap-specific.