Fixed crash on OS X due to clang compiler errors
Fixed crash on OS X due to clang compiler errors

I implemented Roman Lygin's workaround described in
OCCT Mantis 0026778.

Fixes issue #621

BenoitPerrot/oce,BenoitPerrot/oce,BenoitPerrot/oce,tpaviot/oce,tpaviot/oce,tpaviot/oce,tpaviot/oce,tpaviot/oce,BenoitPerrot/oce,BenoitPerrot/oce