GCC 7.1 compiler warnings -Wmaybe-uninitialized on gp_XYZ and siblings

When OCCT is built with GCC 7.1 compiler (MinGw-64) it reports several warnings -Wmaybe-uninitialized in gp_XYZ and sibling classes.

While location of the problem is not properly reported by compiler, the reason is recognized: this is due to usage of local variables of reference type pointing to field of temporray object, like this:

Handle(Geom_Line) aLine = ...;
const gp_Dir& aDir = aLine->Lin().Direction();

Here Geom_Line::Lin() returns temporary object, and Direction() returns reference to its field. The object gets destroyed immediately (compiler has no knowledge of the fact that the value returned by Direction() is reference to field of that object). Thus aDir points to memory where destroyed object was located and which can be easily corrupted.