I again failed to build FreeCAD properly in Solus. But if you really want to use it now, there is an alternate way.
Fortunately AppImage is available for FreeCAD. Download FreeCAD 1.6/1.7 version AppImage from following location.
You need to make the downloaded .AppImage file executable. Once done, double click or right click -> Run to run FreeCAD. No installation required.
I tried 1.7 Git version and it seems working fine in Solus. Please get back to me if you again stuck in some place